Manually adding EXIF data in Bridge

You mentioned wanting to do this in Bridge before adjusting in Lightroom Classic. But the tools for this kind of thing are more readily available as software that extends Lightroom Classic by taking advantage of its support for scripting and plug-ins, for example:

NegativeLab Pro (commercial software) is a plug-in that’s mostly about inverting negative film while also giving you controls to precisely emulate the look of film lab processing, but it also adds an entire film-specific metadata section to the Metadata panel in the Library module of Lightroom Classic:

https://www.negativelabpro.com/guide/film-metadata/#how-to-add-film-metadata

LensTagger is a donationware plug-in that’s another way for you to enter analog film metadata into Lightroom Classic.

https://www.lenstagger.com/documentation/how-to-use-lenstagger/

LRTransporter (free, donation unlocks more features) is a plug-in that “helps you to move your metadata in and out of Lightroom” including “a powerful system for importing data from a CSV file by matching photos that against a particular field in each record.”

https://www.photographers-toolbox.com/products/lrtransporter.php?sec=importguide

So, if you’re willing to do more of the organizational work in Lightroom Classic, one or more of those tools might help you.

I don’t know if anything like those exist for Bridge.

Many of the metadata features in those plug-ins use ExifTool under the hood, so if you’re comfortable using commands in terminal software, you could just use free ExifTool as Erik Bloodaxe suggested, and not have to buy anything. But if you’re not comfortable with the command line, then the Lightroom Classic plug-ins above basically function as easy point-and-click front ends to the same powerful ExifTool commands.

You would need a dedicated exif editor for this. Widely regarded as the most comprehensive is Phil Harvey's exiftool:

https://exiftool.org/