Power of Attorney letter

As a small part of the ongoing farce of my JFRV application, I’m trying to get someone in Hong Kong to take my HK marriage certificate for stamping at the Zhonghua Travel Agency, to avoid having to fly out there myself just to do it.

The (surprisingly friendly and helpful) woman on the phone at the Travel Agency said this was fine, but that my friend would need to have a Power of Attorney letter notarized in a Taiwanese court.

The notarization should be easy, but I have some questions about the actual letter. From reading around it seems like a simple written declaration should suffice, and that I can limit it to only the particular purpose my friend needs it for. However, the form letters I’ve found on the Internet have been very general, granting every possible legal power, which doesn’t seem necessary or sensible.

Will a few lines of plain English with a notarized signature be acceptable?