Update:
So I succesfuly tested new setup with separate regen button and everything seems to work fine. Regen works and delta mode works. I put regen and delta buttons on the same side of handlebars so I ensured that with one thumb I cannot accidentaly push both buttons in same time, so regen and delta switching will never occur at once:-)
However delta mode is very power hungry so with my 30amp settings it is worth only on flats with no wind or downhill in order to go slightly faster. I think that 48V instead of 36V will be better solution for higher speed travel...
