End Point Manager Static & Variable string value?

I’m trying to provision my Grandstream hostnames so that when i look at my dhcp list, i can tell what extension is attached. The P code is 146
I’m trying to set

P146 = x__line1Ext__

so that the host name of line 5123 would be x5123

I’ve been able to successfully set P146 to __line1Ext__ but I’d like to prefix the line number with the character “x” How can i mix these strings in the value field for this parameter? EPM seams to be striping the “x”

If i click on P146=line1Ext and change it to P146=x1__line1Ext__ and click submit, it reverts back to P=146=line1Ext

Is there a way to make this stick?