[Feature] Is this alternative way to set global LaTeX macros possible?

[MrOddlyFormal]

I'm trying to set a \let-type global macro, like they're discussing here. For \def macros I've been using the katex_config.js file, but KaTeX does not yet support the equivalent of \let through the macros object.
KaTeX does support the following syntax:

const macros = {}
katex.renderToString(content, {macros, globalGroup: true})

And this function is what mume uses.

Mume lets us edit the macros object, but I'm looking for a way to modify content. Is it possible? Maybe in the parser.js file?

Ideally, Mume should use a regular macros.tex file for global macros, and content would be populated by it during the call to KaTeX with globalGroup: true. This way users would not have to keep two files for the same thing.

Thanks for the help!