According to Merriam Webster, it is a word, but not one I have ever heard used. Spell checkers also mark it incorrect. In general, there is probably a better word or phrase to use for almost any occasion. One that comes to mind for the dress code example is relax, as in, "In my company they have relaxed the dress code on Fridays", as for the first, I think you would more commonly phrase it as "My manager is thinking about making my work schedule more flexible". Relax would also work in that case, as in "My manager is thinking about relaxing my work schedule", but that might come across as working less hours than before, rather than just shifting hours as implied by flexibility.