I am playing a rogue that I built a little over a year ago for my first ever game of D&D. We play about once a month or so in an ongoing campaign. My DM set my ability scores for me when we began, because I had no idea what I was doing at the time!
I could use an extra point to my wisdom, 13→14. My strength is a dump stat at 10 and doesn't need the boost. (We did 5d6 best 3 for scores.) However, I would like to gain proficiency in Strength saving throws. I want proficiency in Wisdom saving throws too, but that will come once I get Slippery Mind at Rogue level 15 (PHB p. 96).
My question is: can I take the Resilient feat (PHB p. 168) now, to gain that extra point in Wisdom and proficiency in Wisdom saves, and then once Slippery Mind comes to grant me Wisdom save proficiency again, pick another ability of my choice to gain a save proficiency in instead? The PHB says that skills and tools work this way, but doesn't mention this for saves. (There aren't any conflicting ways to gain save proficiencies other than the Resilient feat as far as I know.)
I'd love to know if there's an official rule for this, but if not, I may just have a case to make to our DM.