The reflexive test shows us that although you can find the reflexive form yourself, as in Bless yourself, you can also find the nonreflexive form you, as in Bless you, and these two structures have very different meanings. As is the case with true imperatives, other pronominal forms can occur (Bless {him, her, us}) and non 2nd p. reflexives cannot occur (*Bless {himself, herself}). A tag question test can be appended in one of the meanings (Bless him, won’t you) but not in the other. We must conclude that there are two different structures here. The one that takes yourself and permits tags is a true imperative. The one that permits you and does not allow a tag is an old subjunctive form, meaning ‘May God bless you’. Note the difference below:

Both the true imperative and the old subjunctive permit other pronoun forms (e.g., Bless them), but have quite different meanings.

These are actually main verb instances of have and be followed by participles functioning as adjectives. Furthermore, have and be have nonstative meaning here (‘do such things so that you will {have the work done, be dressed} by the time I get back’).