Taking utrogestan ie progesterone for longer and delaying the bleed in this way is not what is normally understand by having a long cycle. The long cycle is as dazned and I do - ie staying on oestrogen for longer to minimise the time on progesterone. That is the regime that needs careful monitoring, not what you are suggesting, because the endometrium ( womb lining) can build up too much if on oestrogen only for too long.
As Suzyq says you can use utrogestan every day. The point is that Utrogestan - ie progesterone, both changes the lining from proliferative ( growing) which it does on oestrogen, to "secretory" where it changes in structure ready for implantation with fertilised egg and get ready for pregnancy. While you are on the progesterone phase it also stops oestrogen from thikcening the lining any more so it is perfectly safe to carry on taking it.
What I would say though, is that if you are still having a regular cycle and were having heavy bleeds before starting HRT, you may well get breakthrough bleeding at the time you would have had your period anyway - because your own progesterone levels (produced after ovulation by the developing egg) will fall when the egg is not fertilised - thus triggering a bleed (which should be lighter though). Oestrogen in HRT is not high enough to prevent ovulation.
I'm just saying you may not necessarily stop all of the horrible feelings - but may prevent the extreme part of progesterone withdrawal symptoms you have experienced?
Hurdity x