As the others have said. Adding fake hammer marks will not make it look like the real thing. Also - it is hard telling what some of these wax cast steel castings are made from, and a lot of them are pretty brittle. So I don't think propane and a hammer would be a good idea.
What you can do to help the castings is reshaping by filing. Most of the steel castings sold today are much bulkier than original iron hardware. A little thinning and reshaping can be done and you would be surprised how much you can alter the look and get it closer to something that looks right. And at least you will have something that does not look like it came from the same mold as all the other ones running around out there. Spurs on grip rails can be reshaped, bows can be openened up they have a lot of metal at the front, finials can be narrowed and reshaped - lots of things.
Good luck
Guy