Yes, you can certainly do that. Just note that pure CYA dissolves very slowly so could take a few days to show up in the test kit, though perhaps at the higher water temperature it will dissolve more quickly. Technically, you'll be getting more consistent disinfection and oxidation levels from day 1 (assuming at least some of it dissolves quickly) compared to Dichlor-then-bleach where the first days to week when using Dichlor start out at higher active chlorine levels and then decline to the steady-state level when you switch to bleach. This should be somewhat less harsh on hot tub covers, swimsuits, skin, etc. though it's not for very long relative to the time between water changes so not a big deal. The purpose of Dichlor-then-bleach is largely for simplicity since Dichlor dissolves so quickly and many people already have it if they were doing Dichlor-only previously.