Just performed a successful clean install of fsx and pmdgs with sps. I have tried landings at ENVA RWY 09 and RWY 27 both ILS with correct lineup and expected ILS performance. FMC works with AIRAC 1112. (I did a clean install because of major issues with ILS RWY27 ). I'm still not sure what caused it. Should I proceed installing magnetic updates, airac 1113 and pawyare ENVA scenary(makes it more realistic and nice to watch.)? As you understand I'm in fear of messing up ILS navigation if I proceed further. Any suggestions would be appreciated. Can AIRACs be downgraded?

The navdata cannot affect MSFS ILS fidelity, in fact, only the PMDG modules are looking at it. MSFS is not aware of it.Most common ILS tracking problem is due to a registry error that is easily fixed with the registry repair tool from Flight1. I would proceed and if there was a problem try to note what seemed to be the cause.