This is a good idea as long as you are…
A hair long, you are compressing the bearings. A hair short, you are introducing lateral play.
Some time ago I got some long 5mm ID spacers for this exact reason, but haven’t so far attempted to shorten them (and I do not know if I ever will as I started building a stiffer machine). In order to do it square and within a very tight tolerance, ideally you need a CNC lathe.
An alternative little hack could be making a fixture to hold your spacers upright, i.e. by drilling holes with the OD of your spacers. Then, by probing on the fixture’s top face and knowing the fixture’s hole bottom Z, you could mill the excessive length with high precision.