I have two S&W .500 Mags, one with the ILS deactivated, one stock. Can't tell the difference. Email buddy of mine is a S&W engineer, worked on the Model 500 program, said matters not in or out. Don
Levity aside, properly removing the IL will have cause no problems. Plugging the opening will prevent dust, lint, etc. from getting inside the revolver.
If you go to Bullseye Smith's link for buying the Plug, there's a link to a short youtube video that shows precise IL removal.