I have this dilemma when a customer asks me to do something that isn't electrical. If I was putting 40 hours a week doing electrical work, I certainly would charge my regular rate.
But since I don't, I feel like I'm picking up an odd job. Certainly if they want to pay me electrician's rates to hang a shelf, I'll do it. Or if what they're asking me to do is actually more expensive, I'll obviously do it at the higher rate. A good customer asked me if I could hang a shelf in his living room as he was done with the carpenter and didn't want to call him back for this one thing. I told him I'd do it for $40 and he agreed. I was running out of time and told him I'd have to come back to do the shelf. He asked how much he could pay to do it before I left. I told him $100. So I did it, it took me about 15 minutes and he paid me $140 because he thought I meant $100 just for staying to do it before I left.
In your situation, you are doing something practically anybody can do. Possibly you might be better at it since you understand wiring and supports etc, and if you have any creativity you should get paid for that, too. So you might as well charge electrician rates because if you don't, and then you get some real electrical work, you'll most certainly stop hanging Christmas lights to do the other work if it's more profitable. If you can put off some of that other work (besides service calls and calls for installations that are time-sensitive to the holidays) to take care of this time-sensitive stuff, you can make ALL the money.
Just my two cents.
