That's probably why the sidewalks were already correctly mapped as highway=footway, which implies bicycle=no. Adding bicycle=dismount is redundant, but harmless.

This edit will have no influence whatsoever on any routing software. If you see a delivery cyclist on the sidewalk, you may have to consider the possibility that they are acting illegally for a reason which has nothing to do with access tagging in OpenStreetMap.

At least this is a case in which HC Rule 64 actually does apply.