Ghorpm: I don't think you can steal it without guards becoming hostile. But after you choose the path of light (that is after Avlee-Earathia conflict is finally resolved) you can do solve this quest. Don't worry about guards becoming hostile - you won't come back to Castle Gryphonheart. And after some time every area respawns and all your bad deeds are forgotten.
DrSlash: Thanks! But there is one more issue - I don't have any saves before stealing the paintings and I'm in the middle of the quest where you have to choose betweeen helping Erathia or AvLee, so I don't have time to wait - the elven king from the Tulareen Forest will attack Harmondale in less than 30 days. Is that time enough for an area to respawn? Is there any way to respawn this area without waiting (editing saves, perhaps)?
Wait a second! I don't remember anything about Tularean Forest attacking Harmondale. AFAIR during the war you can get five quests:
1. Retrieve plans from the fort and deliver them to the king of elves (helping AvLee)
2. Consult the previous quest with Queen and she will give you fake plans (helping Erathia)
3. Rescuing a spy and bringing him to the Queen (helping Erathia)
4. Consulting the previous quest with the king of elves and bringing a false spy to the Queen (helping AvLee)
5. Final quest - Retrieve Gryphonheart's Trumpet and give it to the side you choose (you can give it to the arbiter!)
If you helped one side more than the other then Harmondale will become a part of this kingdom. IF (and only then!) you gave the trumpet to the arbiter and helped both sides equally a new Harmondale kingdom will be created and you will be an independent lord. But believe me - it doesn't really matter what happens. Only choosing dark or light path has it consequences (and you will get to choose a new arbiter not earlier than 50 days after Gryphonheart's Trumpet quest)
And you can finish the painting quest when it's all over
I hope it helped.
