That's a really good question. King Arthur Flour says: Yes! You can refrigerate with no ill effects in taste or texture, though apple filling will darken in color if there is no acid in the recipe (like lemon juice). In fact, KAF says you can keep the filling refrigerated for up to 4 days or freeze for 3 months!
wow. Did not know that. See this recipe for "Make Ahead Pie Filling":
https://www.kingarthurflour.com/blog/2014/11/23/make-ahead-apple-pie-filling)
DO read the comment section!
BUT! —and this is IMPORTANT—and not mentioned by KAF though it should be...whether you refrigerate those slices or not....you should spread them out to cool on a sheet pan (raised baking sheet; you can cover bottom with foil to avoid having to wash that baking sheet).
You spread the filling out on such a pan and
let it cool completely before refrigerating because If you leave it in the pan (or put it into a container still warm to cool), all slices a-top each other, the apples can steam and become mushy. Spreading them out on a sheet cools them faster, and makes sure they keep a firm, toothy texture that you want in an apple pie.
Please let us know how refrigerating the filling goes and how your first apple pie turns out!