this is most liekly because the voltage is locked in the card BIOS. if one software suite does not allow voltage tweaking, none of them will.
you can flash the cards BIOS to something else compatible, but this is a fairly advanced course of action. a mistake can brick your card.
to be honest though, voltage tweaking a 210 seems pointless. like putting a super charger in a golf cart?
what exactly are you trying to do? even with some insane overclocks, the cards performance will be bad. it will still be just a HTPC card, not a gaming card.