I have owned all 3 at various times. First was the WRX911 (still made today) that does not need the mod, but is a bit more expensive. The R911 Tecsun just lost the slide-switch function after 9 years, and I replaced it with a R9012 recently. Both these two need the mod, and believe it or not, I uploaded a schematic of the R911 a few years back. Looking at that schematic, the AM  coils are separate from all of the SW coils, so the answer is NO it will not affect the SW. Each pair of SW bands has a tap on separate coils.

As far as SW comparison, MHO is that there is little difference outside of set-to-set variance inherent in all of these inexpensive sets. I personally like the knob-style of the R9012 over the wheel of the R911 /MHO.

Regards
Paul S. in CT FN31nl