One problem with a 7-speed cassette is that the spacing isn't exactly the same as 8S, so indexing might not work properly. I've gotten it to work but the cable tension adjustment is quite finicky when doing a mismatch like that.
Originally Posted by
Wolfwerx
Yeah, but I consider that to be a nearly inconsequential (though important) thing to do. I guess it really depends on how often he's going to use the "spare" wheel.
Edited to add: The idea to leave a reminder note is a good one.
Apparently you've never shifted a RD into the spokes of a rear wheel. It's not inconsequential when it happens. OP would have to reset the limit screws and probably cable tension between every swap, not worth it IMO.