I definitely recommend doing it this way. The DIY crowd has been doing it this was for years with no ill effect (myself included). There's a funnel on Amazon that's available for cheap that works PERFECT for the job too: https://www.amazon.com/gp/aw/d/B000EH4V0Y/ref=ppx_yo_mob_b_inactive_ship_o0_img?ie=UTF8&psc=1
IMO, unless you have a pressure pot or pump there is no advantage to gravity filling from the bottom unless the tool you use has a vent. When filling from the top it does go slow but the tool is cheap and easy to use:
https://www.amazon.com/gp/product/B000EH4V0Y
https://www.walmart.com/ip/Hyper-Tough-10106-Transmission-Fluid-Spout/636907435
Once you've drained the trans reinstall the level setting overflow tube and drain plug.
Up top, you plug the hose from the trans filler spout directly into the filter boss and let gravity do the work.
Once the fluid is in, install the new filter and reassemble everything in the engine bay, bring the car up to temp and remove the drain plug, the overflow tube will set the correct level when the excess fluid slows to a drip. Reinstall the drain plug and you are ready to clean up.
*edited to add photos and link