SKIM can be installed on a TJ that did not originally have it, with parts obtained from another TJ (or possibly an XJ) or the Dealership if they still have the parts available. It can also be removed if malfunctioning, which does happen.
There are threads here on JeepForum that detail both modifications.
The SKIM function is programmed into all the ECM's. The only difference is it's either activated or not. Once activated, it can not be circumvented, deleted, or turned off in the computer. If you wish to have SKIM deleted, you have at least two choices. Either buy another ECM that doesn't have the SKIM function activated, or send the ECM to a vendor for reprogramming. It may also be possible to install a SKIM bypass module that is used when installing a remote start system.