Good idea on modding the scart switch.
I modded one of mine with a built in lm1881 sync stripper to avoid having to install them in problematic console's scart cables
Sync stripper mod in the 5 slot Bandridge was cool, at some point I am thinking of getting all these scart switch mods together into one unit - definitely saves time and hassle.
In the meantime, I went ahead and modded the SNES for the 4:3 aspect ratio switch anyway. Basically, I left the +5V on the AV connector as it was and run 9V to one of the S-video pins on the AV connector (I chose Luma) since in the SNES Mini these are also unconnected. So basically a separate 5V and 9V line (the 5V going through a 180ohm resistor located in the cable). On the SNES Mini side the mod was as simple as it gets, but it took me a lot of time on the cable side i.e. basically making the cable from scratch. I was lucky enough to have a fully populated SNES connector from a playasia cable, which I used. I decided on running my audio in a separate shielded cable outside the scart cable from the SNES connector to the scart plug, wired all the grounds, added the caps etc. - happy to say the whole thing is working fine. As for the opened SNES connector, once I ascertained all was good I put some hot glue inside and put some heavy stuff on top - hopefully that will keep it shut.
PS. If anybody is in the market for a good professionally (hand) made NTSC SNES scart cable I would recommend those offered by a guy on ebay going under the name 'gamekingno1' (really modest, I know
). I bought one of these with Csync (he also has cvideo ones if anybody wants those) - these are based on premium quality Bandridge coaxial scart cables and the picture and audio performance is excellent. Only bummer was that his snes connector plug is not fully populated - only has the required pins and its a different design to the play asia / OEM Nintendo one and he also uses hot glue on the snes connector side to seal everything up so this would make any potential modding of the cable pretty difficult.