The Rambam gives us signs by which to identify a proper messianic candidate. If that person performs the enumerated functions (versed in Torah, engages in commandments, enjoins Israel to follow the Torah, fights on our behalf), then it is appropriate to follow their lead, as they are בחזקת משיח (presupposed as the messiah).
The final determination as to whether that individual is in fact משיח is whether they finish the job (i.e. defeats our enemies, builds the Temple and gathers in the exiles).
All of the laws (obligations, privileges, etc.) that devolve upon a king, as outlined through the sefer, would not devolve upon such a person unless they were in fact also actually a king (ideally designated so by a court and prophet). Before such time an individual that is בחזקת משיח but that is not also confirmed as a king would have the same rights and privileges as any other member of the Jewish nation. Importantly it is appointment as a king that has an effect on "halakhic status" (his privileges/duties and the relationship of others to him).
Being בחזקת משיח is more of a barometer by which we may collectively measure a man but does not inherently have halakhic import it is only the additional aspect of actual kingship that does. Furthermore, it would seem that there is some subjectivity in determining whether one is properly identified as being בחזקת משיח (i.e. assessing whether they fit the bill), and accordingly R. Shimon b. Yohai denied the candidacy of Bar Kokhba and R. Aqivah affirmed it. It is only once the individual succeeds or fails that the hazaqah (presupposition) can either be refuted or confirmed.
In terms of applicable law, the משיח (messiah) is no different than any other king. Though it is possible that a future court (may it speedily return) may adjust certain aspects of the functioning of the monarchy. This however is as of yet to be determined.