unmagical , 4 hours ago (edited 4 hours ago)

<span style="color:#323232;">Find: ([A-Z])([A-Z])
</span><span style="color:#323232;">Replace: 1 2
</span>

Click the “Replace All” twice and it should do what you need.

Unfortunately it seems like MS Word uses a non standard configuration for advanced searches so functions like “positive lookahead” are not available. That’s why you need to replace twice.

What TTS software are you using? Is there a way to add pronunciation guides that will apply across all software, not just word?

Edit: Untested:

<span style="color:#323232;">Replace (without quotes): "1 2 "
</span>

This might mean you only need to replace once, but it will add an extra space after acronyms (“PACU” > "P A C U ") and will inject space in mixed case scenarios (“PACUpacu” > “P A C U pacu”).