Wondering how useful putting penetration on a ReTe teleporting effect in my Talisman. Good vs PeVi, wards, Aegis, hostile Aura's but if a hostile magi can just take hold of it and protect it with his Parma then it starts to be necessary.
It it is a small item it will be protected by his MR. A large item will only be partially covered by his MR.
Anyone (including yourself) trying to cast a spell or similar on that talisman will need to penetrate whatever MR protects it - which might be the MR of the hostile mage if his MR covers the whole item, and the item's innate MR (your Form bonus) in either case.
Not really any other different from other cases when someone has Magic Resistance from more than one source - like for example a mage carrying a relic. The highest MR applies, unless the rules explicitly say the sources stack.
No, no more than a spell you may cast on him with Touch range would bypass MR just because you are touching him.
Same with something like an enchanted ring that someone wears (that isn't their talisman) - it would need to penetrate the wearer's MR to affect them.