Sounds like the kind of thing you've done with "translating" into a "generally useful" feature.
Yes, that's it exactly.
And yes, if it's too hacky, by all means decline the gig. Or better still, make recommendations for a correct implementation that you'd be willing to do, instead. Be sure to include arguments as to the greater maintainability and less of a headache for them if they decide to spend a bit more and do it the right way. Most companies will agree if the difference isn't excessive. As for those who don't, who needs them?