A few lines of code and you have your own object cloner

Class DC.ObjCloner [ Abstract ]
{
/// obj: Cache/IRIS or a Dynamic(JSON) Object
/// 
/// For simplicity, JSON-Types null, true, false, etc. are ignored
ClassMethod Clone(obj)
{
    if $isobject(obj) {
        if obj.%IsA("%DynamicAbstractObject") {
            if obj.%IsA("%DynamicObject") { set new={},arr=0 } else { set new=[], arr=1 }
            set iter=obj.%GetIterator()
            while iter.%GetNext(.key,.val) {
                set:$isobject(val) val=..Clone(val)
                do $case(arr, 1:new.%Push(val), :new.%Set(key,val))
            }
            quit new
            
        } else { quit obj.%ConstructClone(1) }
    } else { quit "" }
}
}

Class DC.Import Extends (%Persistent, %JSON.Adaptor)
{

Property thingone As %String;
Property thingtwo As %String;
ClassMethod Test()
{
	// create a test stream
	set myStream=##class(%Stream.TmpCharacter).%New()
	do myStream.Write("[{""thingone"":""Red"",""thingtwo"":""Green""},{""thingone"":""Blue"",""thingtwo"":""Yellow""}]")
	
	// convert input (JSON) stream into a JSON object
	set data={}.%FromJSON(myStream)
	
	// loop over the JSON-Array and import each array element into your database
	for i=0:1:data.%Size()-1 {
		set obj=..%New()
		set sts=obj.%JSONImport(data.%Get(i))
		if sts set sts=obj.%Save()
		if sts continue
		write "Error: i=",i,", reason=",$system.Status.GetOneErrorText(sts),!
	}
}

Of course, instead of "myStream" you should use your REST-input stream.

do ##class(DC.Import).Test()

zwrite ^DC.ImportD
^DC.ImportD=2
^DC.ImportD(1)=$lb("","Red","Green")
^DC.ImportD(2)=$lb("","Blue","Yellow")

If you want, for whatever reason, to compute the CRC of a Stream then write an short method like this (or use this):

/// Input : str - a sting or a stream
///         typ - CRC-Type (0..7, See ISC documentation)
///         
/// Output: crc-value
/// 
ClassMethod CRC(str, typ = 7)
{
    i $isobject(str),str.%IsA("%Stream.Object") {
        d str.Rewind() s crc=0
        while 'str.AtEnd { s crc=$zcrc(str.Read(32000),typ,crc) }
        ret crc
        
    } else { ret $zcrc(str,typ) }
}

Where is the problem?

Is my assumption correct, you use for the property "PrijsAkCatVm" an own data type (Asci.Getal) instead of %Numeric, in order to be able to use some extra parameters like HINT, VIEW, VISIBLE etc.
Is that correct? If yes, then there is a much simpler solution where neither  MS nor SQL won't stumble over it. The catchword is PropertyClass.

/// Create a new Cache class.
/// Define here all the extra parameter you need.
///
Class Extra.Props
{
    Parameter HINT;
    Parameter VIEW = 1;
    Parameter VISIBLE = 1;
    Parameter VOLGORDE;
    // etc.
}

/// then take your Cache Table, add the above defined class
/// to your Cache Table, complete the property definitions with
/// the appropriate parameters - Done.
///
Class Your.CacheTable Extends %Persistent [ PropertyClass = Extra.Props ]
{
   Property PrijsAkCatVm As %Numeric (CAPTION="...", "HINT=...", etc.); 
}

Now you can use the above defined (extra) parameters in each and every property  in this class.

There are two aspects of the question,
a) how to get the old property value of a modified property and
b) what happens, if one still opens the same object in the SAME PROCESS once again.

For a) the answer is already given by either using the GetStored() method or cloning the object. In cases, where an old propvalue is needed, I prefer the object cloning, especially if the base object contains embedded objects.
Of course, if the application uses the %Reload() method, then the %OnReload() callback method should do the same as %OnOpen() does.

Class DC.Data Extends %Persistent
{
Property Name As %String;
Property Addr As DataAddr;
Property oldObj As Data [ ReadOnly, Transient ];
Method %OnOpen() As %Status [ Private, ServerOnly = 1 ]
{
    set r%oldObj=..%ConstructClone(1)  // do a deep clone
    do ..%SetModified(0)               // clear modified state
    Quit $$$OK
}
}

Class DC.DataAddr Extends %SerialObject
{
Property Street As %String;
Property City As %String;
}

kill
set obj=##class(DC.Data).%New(),obj.Name="Joe"
set obj.Addr.Street="Abbey Rd. 123", obj.Addr.City="London"
write obj.%Save() --> 1

kill
set obj=##class(DC.Data).%OpenId(1)

set obj.Name="Paul"
write obj.Name --> Paul
write obj.oldObj.Name --> Joe

set obj.Addr.City="London East"
write obj.Addr.City --> London East
write obj.oldObj.Addr.City --> London

For b), it was said, that a second open (of the same object) returns the same OID. This is true. But there is one more thing. That second open doesn't even trys to get that object from the database but just keeps a lookout in the memory. This means two things (assuming no locks are used)
1) if the object was modified by another process, you "open the old version" already in the memory of your process, and
2) nevertheless that an other process deletes that object, your proces will open a nonexisting object...

Seq  Process-A                                  Process-B
-------------------------------------------------------------------------
 1   set obj1=##class(DC.Data).%OpenId(1)
 2                                              do ##class(DC.Data).%DeleteId(1)
 3   write ##class(DC.Data).%ExistsId(1) --> 0
 4   set obj2=##class(DC.Data).%OpenId(1)
 5   write obj1=obj2 --> 1
 

As a consequence of the above, I have learned not to use a simple open:

set obj=##class(Some.Class).%OpenId(oid)

but a more secure open, by invalidating a possible old instance:

set obj="", obj=##class(Some.Class).%OpenId(oid)

My favorit is

write $tr($zd($h,15),"/.")

Instead of ZW RECORD (which only gives an ASCII rubbish) please give some examples as hex-dump (ZZDUMP RECORD or something similar). A few values together with hex-dump.

Merely you have to "open" the article to get those tags into top position. If you just browse (see the screenshot) over the articles: (a) you have to scroll down and (b) a tag name could have but must not have the same meaning as an acronym. In my opinion, an acronym should always be explained after the first usage - either you write it out or you insert a link or whatever...  

Excuse me, but it's a bad habit to introduce something with an acronym without saying what that acronym  stands for.  The site:  https://acronyms.thefreedictionary.com/CCR  lists 241 possible meanings for CCR. Which one is yours?