Mediabox editor may not have the 1000 transponder limit, but it does have a 400 Provider limit. I imported my tp_prog.abs (from Skybox M3, renamed from .dbs) and just deleted any providers in the list after 400 - it wouldn't save or export otherwise.
But it's been doing my head in. I get my Fav channels in the desired order, save as an .si file just to be on the safe side, then export as Ali gen nocas to TP_prog_list01.abs. If I re-import the same file, I find that the Fav channels are now arranged by order of transponder - all my good work undone! And it's the same story if I rename the file and import to my box. I tried repeatedly and found no way to stop it re-ordering by transponder.
So then I tried the split and merge technique, but after editing sat_tp_prog.udf in Mediabox I get a data error when merging.
So then I installed the trial version of Setedit HD100 and edited sat_tp_prog.udf in that. Luckily I didn't have to make too many changes because you're limited to 20. I kept saving after every edit and when I reached the limit, closed and re-opened the file. It's a bit awkward because the Fav names are not displayed at all - not even "Fav list 1", just a blank space - you have to guess which category is which if you modify a channel's attributes. Anyway, editing complete, I merged the file successfully with sat.rom and uploaded TP_prog.dbs back to my M3. Success! Finally I have my Favs sorted as I wish.
(And thanks to AJ for providing the initial list!)