Is converting a font licensed for use as a web font to WOFF2 generally considered to be modification?
My primary concern is with fonts licensed under the SIL OFL. There is a caution in the guidance for the licence that an irreversible conversion to WOFF constitutes a modification, so if I need to create a WOFF for somebody else's font, I first check that back conversion to TTF/OTF yields the same font. (On a very small sample set, I haven't had the problem yet.) However, there seems to be a far greater likelihood of a conversion to WOFF2 not being reversible. If one creates a modified font under the SIL OFL, one has to give it a new name, and propagate the licence.