The you will need to split the output from the form and add the extra parentid's, then rejoin.
here is an example of how to do that, using lowcode
[{"id":"ccd289245bc6e3fd","type":"inject","z":"d1395164b4eec73e","name":"","props":[{"p":"payload"},{"p":"parentID","v":"urn:zz:xx:cc:","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"","payloadType":"date","x":180,"y":2600,"wires":[["0c233c81a6f78369"]]},{"id":"0c233c81a6f78369","type":"template","z":"d1395164b4eec73e","name":"","field":"payload","fieldType":"msg","format":"handlebars","syntax":"mustache","template":"1\n2\n3\n4\n5","output":"str","x":340,"y":2600,"wires":[["058b14a2ba795850"]]},{"id":"058b14a2ba795850","type":"split","z":"d1395164b4eec73e","name":"","splt":"\\n","spltType":"str","arraySplt":1,"arraySpltType":"len","stream":false,"addname":"","x":470,"y":2600,"wires":[["0a4935fe856528c0","5be0ec1be8794121"]]},{"id":"0a4935fe856528c0","type":"template","z":"d1395164b4eec73e","name":"","field":"parts.ch","fieldType":"msg","format":"handlebars","syntax":"mustache","template":"{{{parts.ch}}}{{{parentID}}}","output":"str","x":400,"y":2660,"wires":[["d03d33dac6ad19e0","5be0ec1be8794121"]]},{"id":"5be0ec1be8794121","type":"debug","z":"d1395164b4eec73e","name":"debug 2461","active":false,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","statusVal":"","statusType":"auto","x":630,"y":2560,"wires":[]},{"id":"d03d33dac6ad19e0","type":"join","z":"d1395164b4eec73e","name":"","mode":"auto","build":"object","property":"payload","propertyType":"msg","key":"topic","joiner":"\\n","joinerType":"str","accumulate":"false","timeout":"","count":"","reduceRight":false,"x":530,"y":2660,"wires":[["cbcf34e525bff31d"]]},{"id":"cbcf34e525bff31d","type":"debug","z":"d1395164b4eec73e","name":"debug 2460","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"payload","targetType":"msg","statusVal":"","statusType":"auto","x":670,"y":2660,"wires":[]}]
You could also split in your function then append the id's to the last four and rejoin to.