well I often think of the old /traditional Songs ,rather like old paintings,or antiques,
if they have had to have the work of a restorer,to enable me to appreciate their beauty[even if they are no longer original]so be it.
   The version I sing of Game keepers lie sleeping[thatBob Roberts sang],I suspect is a rewrite,But it is in my opinion the best version,and that is what I look[Iam sure you do too] for when I am singing,It doesnt worry me that it may or may not be traditional,it has the best story,and has been lovingly restored in a suitable style.
If I view a painting,in a gallery,My enjoyment comes from the beauty that I perceive [at that moment in time],if it turns out later to have been a very good forgery,my enjoyment hasnt been ruined[many art experts and galleries have been fooled,there was a very good art forger in the 1960s ,his name escapes me,whose work was as good as the original artist.
Traditional/old songs have evolved and do change,the problem we face now,is that with the increase in communication[computers],these changes will no longer be anonymous,but we shouldnt reject the changes[because its tampering with an original] if they are an improvement [famous flower of serving men,Gamekeepers lie sleeping].
I have to disagree with you,what you are doing is analgous to the traditional process,and will be the way, traditional/old songs will be kept alive in the future,if you are un comfortable with doing this all you have to do is mention your amendments when you introduce the songImight add that youare an ideal person to be making alterations as you are steeped in the tradition.Dick Miles