As an alternative you can put your homebrew app on your home screen.
According to a reply in this post you can run homebrew apps directly from the home screen.
https://gbatemp.net/threads/homebrew-menu-nsp.516236/
Before tinkering with the eshop button, do make a NAND backup because this can mess up your Switch badly.
About repurposing the eShop button :
You can change the Homebrew menu from Album to eShop according to this post :
https://gbatemp.net/threads/use-eshop-as-homebrew-instead-of-album.521561/
The titleID for the eShop is 010000000000100B.
You can try bluntly overwriting your eshop application but I assume there are some checks in the titleDB.
Another possibility would be to check if it would be possible to run a second homebrew launcher that launches your NRO instead of the homebrew application.