First thing I would do is find a chrono...to save gas. hehehe.
Sure you can cut a spring, I do it often. I even warm up the cut end, bend it a bit to flatten out the contact area, then grind it flat so it will sit nicely on the spring guide. A bolt gun is way more forgiving than an aeg for spring work in that it cycles way slower and the spring has a moment to seat before letting it fly.
I also found in my L96 it was hard to find a spring that would get it to the desired fps, so after some tuning, we're around 480. Ideal for our field and the weight of BB's used. By trimming the spring you can zero in to your target velocity quite well....but I would only take off one coil at a time, check it for a few dozen shots so it seats in, then do it again. Time consuming, but good results.