How much shorter you can feasibly go depends on some design factors... current profile, length of stiff handle section and working limb length, whether it's taken any set yet and where, etc. I've made trilams as short as 58" ntn and over 60# @ 28".
I wouldn't use heat to bend them, but if the limbs are down to working limb thickness, you could reflex the outer limbs more by cutting into the limb with a bandsaw creating a kerf through the limb, and then gluing in a short lam of appropriate thickness to fill the void, bending into more reflex during glue up. Whether it's a practical thing to do is a judgement call on each bow.