How to select a particular formatter among many?

[V4G4X]

Suppose I have a bunch of formatters available.

1. yamlls (General YAML, From Mason)
2. spectral (For OpenAPI, From Mason)
3. cfn-lint (For AWS CFN, installed by Mason, enabled by null-ls using null_ls.builtins.diagnostics.cfn_lint)
4. Prettier (General case)

How do I?

1. Set a default formatter for a file type.
   Is it possible to override this at a workspace level?
   So that spectral is the default for one project, and prettier is the default for the rest?
2. Run a one-off format command with a particular formatter?
   So cfn-lint may be set as the default formatter, but just this once I want to format the file with prettier.

I think I may be asking for a lot but this seems like a common use case, especially if you come from VS Code.
Please let me know what can be done!

[srghma]

I wanted to replace alejanda formatter with nixfmt

I found it was defined here https://github.com/AstroNvim/astrocommunity/blob/c4903b23b75c0a429ebe02e1d31d1a8316d9691e/lua/astrocommunity/pack/nix/init.lua#L18

so, I forked