Roms like pureness 1 and Honamiutreized are strictly firmware specific that is why, i think those developers specifically state do not flash this over other firmware variants that will cause problems and this is because those developers have heavily modded the latest firmware to add more tweaks to give advanced user experience hence that ROM may not be compatible on older firmwares.
But probably you can find Custom Roms (Like Cleaned and Tweaked Rom, JBXSP Rom, Project AOSP Rom) based on 2.245, just go to respective threads and check, you will find that the most of the ROMs' version 2 or 3 should be based on 2.245 firmware.
Try and enjoy customs roms.
No if you check this link http://forum.xda-developers.com/show....php?t=2311964
you can find many FTF for 2.254 which can be flashed using Flashtool and have latest firmware and flash latest ROMs based on 2.254 without any problem.