Symbol to replace _ in registry

What symbol should I use to replace _?

I wish to change the variable, RDD.1.ABC_01 to run as Interactive User instead of Launching User.

Registry:
SOFTWARE\Classes\$Name\CLSID

Coding:
WriteRegStr HKLM "SOFTWARE\Classes\APPID\$ReadRegistry" "RunAs" "Interactive User"

The program is not able to change it to interactive user but if I change the name, RDD.1.ABC_01 to RDD.1.ABC, it would be be to work.

So is there any symbol I could use to replace _?

Are you sure underscores aren't supported? It works fine for me with regedit.exe. If they don't, it's up to you what to use instead. I don't know of any convention for this. I'd use a dash, if I were you.