I can write well with a glace icing, but it has to be very stiff, and I'm not up to that this week (I've got Rheumatoid arthritis, and I'm in the middle of a flare-up right now) Since I can only work with my hands for a few minutes at a time, I was hoping I could write the messages on parchment paper with royal icing, let them dry, then apply them to my cookies that have been flooded with glace icing... does anyone know of any reasons this may not work? Thanks so much!

don't know if it will work but that paper isn't edible and would have to be pulled off to eat cookie.
How about rice paper???? You can eat that. I use to use royal icing to attach the paper to a cookie.
then there is always thin fondant squares you could write on or better yet make a chocolate square.
don't know if these ideas help but I thought I'd toss them out for you to think about.

Yes, you could easily pipe the lettering onto the parchment and, when dry, peel off and attach to the cookie with a dab of icing (either glace or RI). To save your hands, though, have you considered using food color pens? You'll have to make sure the glace has fully dried before doing the writing. And then be sure to let the food color dry before bagging or stacking so you don't smear the writing.