But if you need to replace multiple things it will be inefficient as it will loop over the string multiple times, and allocate and copy multiple times.
If that is the case, and speed matters, I'd use askama or display-as or even just convert the file into an inline rust string literal and use print!().
I have been busy making templates and the largest on so far has 18 substitutions. So I think I'm going to go with one of the templating systems rather than regex. But which one is easiest for a beginner?