Ok... Let's see now. As for the first problem, the unit must be summoned. So if the unit is not summoned you cannot put a timed life. But if you can you can just make a trigger, and depending on what circumstances you want the unit to have the timed life make the whole events, conditions you need and put at action Unit - Add expiration timer. That should do it. BUT REMEMBER THAT THE UNIT MUST BE SUMMONED!!! You can edit this at the Object editor, the unit you want. If you want this to work on any unit... Tell me what the spell is like and I might help.
The second problem sounds familiar. If I remember well, I was trying to make a furion who can turn into a bear, but this would be based on another skill, the Goblin Tinker's. Your's is different I guess. I'll try to remember what was the problem.