If it were possible, you would "lock yourslef out of CHDK". I mean, if you switch to "no CHDK", how could you possibly switch back to CHDK?
you don't say what you are trying to obtain, and what problem you have with CHDK loaded, but there are several VERY simple solutions:
1) disable CHDK autoboot, and load CHDK only on request
2) have two SD cards :-)