It seems it is possible.

Here in the following picture you can see the final results of my work in the last weeks:

In the dialog box, you can see I managed to show accented vowel (non standard characters): è, é, ì, ò, à, ù, that are necessary (but not indispensable, actually) to translate adequately in Italian. Virtually, one can modify the fonts file(s) replacing unused gliphs like “<“, “>”, “$”, “%”, “&”, “#” with edited ones. So I did, succeeding in compressing them and in replacing in global.hag file.