Can I do 100% water changes for a small betta tank?

I had a betta in the smaller tank for a while before I learned the horrors of them. But yes, you can do 100% changes often, just make sure to add a tap water conditioner. I had a beta in a .5 gal for almost a year with 100% water changes every week, and he was a healthy bugger! Now looking back, I have no idea how he was alive and healthy for so long. Yikes! Anyway, good for you on getting him a bigger tank. I am sure he will be fine until his new tank is ready.