I sewed zippers into the hips of my OG prana Zions and it was pretty easy even though it was one of my first sewing projects. They don’t look professional at all, but they’ve held up for over a year of hiking and hunting. I would think any local seamstress or knowledgeable family member could do a pair of pants in under an hour.
I haven’t done it but my wife and mom both know how to sew and either could do it in probably minutes. It would be pretty simple for anyone with any sewing skills.