So the code to change the number of arguments is fine.  What's wrong is the code to store the error code.  That comes /after/ the three byte call primitive bytecode at the start of the method.  So it should read

xpc := self initialPC + 3.

"long store temp"

(self at: xpc) = 129 ifTrue:

[self at: xpc + 1 put: (16r40 + numArgs).

self at: xpc + 3 put: (16r10 + numArgs)]

Is there any solution to make it working?

The above should work.  But there's a much easier way