The Professional edition of FontCreator is ideally suited to a task like this. You can use complete composites to create your several versions of each letter, as one normally does for à á ã á ä ā and so forth.
You could perhaps replace each accent with one, two, or three horizontal lines, and use the built-in CompositeData.xml file to generate your special composite characters, but Unicode code-points are not assigned for all possible combinations of a-z and accents, so you would need to add some more.
CompositeData.xml is a plain text file that can be edited to add your own custom assignments to create your custom composite characters in the Private Use Area. FontCreator already does this to create Petite Capitals with accents in the PUA. Run the Transform Script from Tools, Glyph Transformer, Open, Petite Capitals script on a standard font to see it in action.
Alternatively, you can just use copy and paste to create composites, which may prove to be much less work, unless you’re planning to edit several typefaces in the same way, e.g. regular, bold, italic, and bold italic, for both Serif and Sans Serif fonts. See my tutorial on Complete Composites to see how to do this.