It would be nice to have the option to manually populate specific table cells, in order to add irregular forms that cannot be automatically generated (done!), or to indicate that a particular form doesn't exist (i.e., that this particular lemma has a defective paradigm).
Shouldn't be to hard to implant, in theory already possible by placing a hypen or simular charactar as an irregular form. Submiting an empty irregular form will just result in the regular form (again), there should be found a way to combine both features. Maybe just as a switch in the irregular table form.