If you are just looking to try out different length stems to see what they do for you, then you might consider changing to a threadless adapter so you can use a stem for threadless headsets. Then you only have to undo the 4 tiny bolts on the endcap of the stem to change bars. That'll end the annoyance of having to remove the bar tape and brake levers or dual control levers. And though I haven't looked for a "7" type stem with quill in ages, I'd think you'd have more choices available with threadless stems.

As far as shortening the stem or lengthening it, that is mostly for adjusting your reach to the bar where your hand positions are. While you might feel the bike handles weirdly the first ride or two after changing the length, that is something you'll get use to. You muscle inputs and timings have to adapt to the new setup.