I may have a tool that could be useful for you roger64, if you wish to give it a go.
Attached is my WIP tool which has a basic frond end to quickly perform some font related tasks, including enboldening fonts.
The tool basically calls fontforge to perform the actual changes.
To run it, you need a recent build of fontforge (late 2015 or younger). If you have Calibre installed, you don't need anything else. Otherwise you will also need to download Python 2.7/3.x, and PyQt.
To run it using calibre, at the command prompt, run:
Code:
calibre-debug path/to/ReadifyFont-Qt.py
Otherwise, with python and PyQt installed, you should be able to run the script directly.
Note that this is a WiP build that I haven't worked on in months, and remains unreleased, so there will probably be some bugs. There is no guarantee that the preview functionality works properly, and that feature isn't really complete anyway.
To use it, load up to four files (regular, italic, bold, bold italic), check the font variant in the drop down box matches the font file loaded, Give the font a new name, choose options related to kerning, PANOSE etc, and choose how much to embolden a font by. I personally like using 12-15. 50 is considered "bold". Adjust it to your personal taste.
Also note, that only regular and italic fonts will be emboldened. The tool will not modify the weights of bold or bold italic, so you can safely load all variants to give them consistent names and options.
EDIT: Updated the zip file to fix an error that meant TTF files couldn't be loaded.