It's tricky, isn't it? Just waggling a rod in a shop doesn't really tell you that much and not too many shops stock extra long float and trotting rods anyway.
If you're confident with putting new rings on a rod ( I can just do it, but it doesn't look pretty!), then why not give it a go then?
One 'trick' you might try is to thread your line only up to the nearest ring where you are thinking of cutting the tip section and try a few casts in the garden. You'll get some idea about the rod action if you cut at that ring before you actually reach for the saw! You can also try striking against your line tied to a bit of garden furniture and see how the rod still protects your hooklength ( or not! ) I'd imagine the rod will only work for heavier hooklengths after you cut the tip down?
As to the butt section. You could turn it over if it uses reel bands and tape new rings on the 'wrong' side to try the spacing out. I think Preston rods use screw down reel seats though, don't they? If so you're going to have to cut it all down before you do much
You can get new foam grips and reel seats from Hopkins and Holloway and theyalso have another site on the 'net called Guide 'n Blanks, more specifically aimed at rod builders.
Hopkins Holloway - specialist fishing tackle and fishing tackle components - Seymo, Fuji, Stonefly, Tomlin
Fishing rod blanks and guides - buy online
---------- Post added at 11:46 ---------- Previous post was at 11:42 ----------
How rude of me! I should have wished you the best with your wrist injury. I had some problems once, probably caused by servicing light aircraft which seem to be held together with self-tapping screws.
My GP sent me to a clinic where a beautiful nurse worked the joints and gave me ultrasound treatment. It worked! If I'm ever troubled again, which is very rare, I can work the joints loose again.
I hope you have the same good luck and a rapid recovery.