Currently it does not seem like there is much in the way of doing this. @BarbuDreadMon I believe is the one who could say more on it, though.
Per this reference, on May 3rd 2021 FBNeo - Libretro
“* Macros : First, some words about macros, the reason macros from standalone aren’t supported is because there can be dozens of them for a single player on a single game, however you currently can’t map that many actions with the Libretro API (and this is not only a problem for macros, handling service menu when it involves several buttons can be tricky too) because all inputs need to be assigned to a button from the get go. In the past, there was some workaround for this through core options, but it had its own share of issues so it was removed later. I recently decided to re-implement support for a select few macros, for now it only includes 3xPunchs and 3xKicks on SF-like games but implementing a few more could be done if I can get some help sorting out the ones that’ll be the most useful so that they’ll fit within the RetroPad model.”