Can I make this but use a crumble for the top crust? I have extra pie dough from a different day, and wanted to use it for this!

I don't know why you can't. I love crumble crusts on fruit pies.

What a great idea! Of course you can. Let us know how it turns out.
mmmm... crumble crust. Runs off to make rhubarb crumble.

Absolutely. I like using this recipe for rhubarb pies:
1.5 c. flour
3/4 c. brown sugar
1/4 c. granulated sugar
pinch of salt
dash of cinnamon or ginger
12 tbsp butter (cold)

Mix everything together with a pastry knife, then crumble together with your hands. Adding slivered almonds, pecans, walnuts, or oats is also great with this crumb!