I think, the idea using a patch/update instead of every time make a complete new installation of the game, is the right way !
Regarding the update problems:
Why not just pretend that the Update.exe needs to be copied into the SexSim installation-folder and executed there?
Then it would not matter which path was Sexsim installed, no need to search the registry, etc...
this would require moving the updater to the sexsim folder, either manually -which may not be possible without 'administrator approval', and leads to tickets like "
I tried moving the updater to the install folder but got access denied"- or automatically which requires the use of the registry to locate the install folder.
however neither one of these methods would fix the problem of the installer not correctly identifying the updater when ran.
another method would be to simply write the data to the current folder without performing any checks, but then someone would say "
I installed the update but am still on the old version" (update installed in the Wrong location) or "
I installed the update and it overwrote the pictures of my grandma!" (update installed in the More Wrong location).
this sort of highlights one of the problems that software developers deal with, there are many different types of people, and many different types of environments, and building a single thing that works for everyone is very difficult.
a bit like designing a vehicle that can fly in the air, sail on the water, and drive at highway speed