Changeing choices and defaultvalue of cdfParameter through callback

I have a question regarding the change of choices in an cyclic cdfParameter as well as setting a new defaultvalue using a callback from an other parameter when creating PCells with SKILL.

Right now i am working on a design where I have a cyclic parameter, which sets a metallayer. According to this parameter a second cyclic parameter should only have the options of the metallayer above and below the first parameter. For example when the first one is using M4, the options of the second parameter should be M3 and M5. I achievd this using a global variable (I know, that this is bad), which means that when I restart Virtuoso, the state is lost, because the global variable is unknown. And also when opening a second design and using the generated PCell the global variables are already set to the values of the first design. A code example would look like this.

library = ddGetObj("examplelib")
cell = "examplecell"
layeroptions = list("M4")
Lay = "M4"

PCellLayoutId = pcDefinePCell(
list( library cell "layout" "maskLayout")
; Parameters
    (
    (layer1 "M3")
    (layer2 Lay)
    )
    let(()
        cv = pcCellView
        dbCreateRect(cv list(Lay "drawing") list(x1:y1 x2:y2))
        dbCreateRect(cv list(layer1 "drawing") list(x3:y3 x4:y4))
    )
dbSave(PCellLayoutId)
dbClose(PCellLayoutId)

let(
    ( cellId cdfId ) ; searching the cell name
    unless( cellId = ddGetObj( library~>name cell )
    error( "Could not find cell %s." cell ) ; error, if cell not in library
    )
    when( cdfId = cdfGetBaseCellCDF( cellId )
    cdfDeleteCDF( cdfId )
    )
    cdfId = cdfCreateBaseCellCDF( cellId )

cdfCreateParam(cdfId
    ?name "layer1"
    ?type "cyclic"
    ?prompt "Layer 1"
    ?defValue "M3"
    ?choices list("M1" "M2" "M3" "M4" "M5" "M6" "M7" "M8")
    ?callback "layeroptions = list(\"\")

   
    ; (this code kills the submission mask of the support website)

    print(layeroptions)
    cdfgData~>layer2~>choices = layeroptions
    Lay = \"\"
    "
    )

cdfCreateParam( cdfId
    ?name "layer2"
    ?type "cyclic"
    ?prompt " Layer 2"
    ?defValue Lay
    ?choices layeroptions
    ?callback "
    Lay = cdfgData~>layer2~>value
    print(cdfgData~>layer2~>value)"
    )

    cdfId->simInfo = list( nil )
    cdfId->simInfo->UltraSim = '( nil )
    cdfId->simInfo->ams = '( nil )
    cdfId->simInfo->auCdl = '( nil )
    cdfId->simInfo->auLvs = '( nil )
    cdfId->simInfo->cdsSpice = '( nil )
    cdfId->simInfo->hspiceD = '( nil )
    cdfId->simInfo->hspiceS = '( nil )
    cdfId->simInfo->spectre = '( nil )
    cdfId->simInfo->spectreS = '( nil )
    cdfSaveCDF(cdfId)
)

Is there an intentional way to change the parameter options and defaults without using a global variable? And if not, does anyone have an idea how to change the options without using the global variables?

Thanks in advance, any help is appreciated.