I already tested .. rebooted to new twrp by powermenu after a long time , flashing rom , wipe cache and dalvik , reboot to system ..
Worked like a charm ..
After booting to system , trying to reboot to recovery by powermenu , still working fine and still decrypted ..
I think everything is great now ..
NOTE
In case you already flash new twrp..
I have to tell that new rom will contain a recovery.img file inside firmware-update folder , if you don't want to loose the new twrp you have to delete recovery.img from this folder or replace the recovery.img with the new twrp by renaming it to recovery.img ..
EDIT
@Iain_B
Well you can't miss it now , as you can read at below post after installation of new rom , twrp will be changed , so you don't have to do more than flashing new weekly update..