Built an installer for IMT 1.5 and installed it on Endive and Chicory. Seems to work OK. I opened and re-saved all the old files using it, in order to get rid of the old appDesc blocks, and then re-edited them to change the schema filename to mariage.rng. In future, it shouldn't be necessary for any version of the IMT to mess with schema processing-instructions, so future upgrades should be less problematic.