in c51 you can set memory model for each "procedure" and set memory model of "program"

but:

how change mamory model of "program" in runtime !

for example in my program require start with only internal memory(256 byte) for cheaking and initializing program and if fault in xmemory report it.
but internal memory model such as "local stack" is very low for running main program contain in main.how change it for run program

how do it ?