I have a question about the inflection of participles formed from reflexive verbs in Latvian (e.g. darbojošies, sauļojies). Can any of them combine with the comparative suffix (-āk-) and/or the definite adjectival endings (-ais / -ā)? Thanks!
It doesn't make much sense for comparative degrees in this case. I don't think that any participles can take -āk- suffix except in some cases when the line between the verb and adjective is fuzzy and such participles have become true adjectives, for example, aprakstošs – aprakstošāks. I don't think that it can happen with the reflexive verbs though. The participle darbojošais has limited usage and often it is better to replace it with some other phrase. There is a common phrase darbojošās personas (acting persons) that is a standard set expression but darbojošais uzņēmums (acting enterprise) sounds very colloquial. One can often find such phrases in bad translations.
Participles of reflexive verbs doesn't have definite endings. Although it is common to find such attempts in colloquial speech. For example, from piedzerties (to get drunk) one can form piedzēries cilvēks (a drunk person). However, the form piedzērušais cilvēks (the drunk person) is nonstandard. Not possible in the literary language because this could be understood the participle with the definite ending from piedzert that means something different. Non-reflexive verb participle should be used in this situation, for example, iereibušais cilvēks (the intoxicated person).