As the topic says: I have a H-S-H Ibanez but I don't use any other pickup than bridge. I'd like to put EMG81 in there but I've heard its a real pain to use passives and actives at the same time. So is it possible to disconnect the passives and just install that one emg?

I'm not too good when it comes to cables and stuff but I don't really want to take it to the luthier, its a rather cheap guitar but plays nice. Is it possible to do it myself?
i can't see any reason why that wouldn't work ^^ (disconnecting all the passives and install active in bridge). Well if you have enough space to put battery in ^^
Do I have to change/remove the 5way switch or it just won't work at the other positions?
You won't need to connect anything to the 5 way if you only have one pickup. Look on the emg website for wiring diagrams for single pickup with one vol and one tone. The solderless install couldn't be easier.