Alessandro if you use a Paterson or other translucent reel it is possible to re-expose while the film's still on the reel.
I do have manufacturers chemical reversal baths, also Fogging Developers, some of the chemicals are not that easy to get hold of. I'll have to dig them out, I've not put them in my database yet. There's Kodak FD-72 which uses sodium dithionite, but it's not very stable once mixed and only lasts a couple of hours. Stannous chloride and derivatives of hydrazine can be used and also Sodium Sulphide or alkaline Thiourea (Thiocarbamide). I'll post some ideas for you as soon as I get time to sort them out.