In Cicero's "ad Familiares" 12.10.2 there is:
"quem quidem ego exercitum quibuscumque potuero rebus ornabo;" =
"This army, indeed, I will compliment by all the means in my power." (Perseus)
Why isn't the accusative, (from "ornabo"), "this army", given as, (masculine) "hunc exercitum"; why use a relative pronoun, (masculine, accusative) "quem"? This, usually, introducing a relative clause would be deployed for something like, "The army (nominative) which ("quem") I will compliment". In this example, such translating does not apply and "the army" ("exercitus") is in the accusative, "exercitum", anyway.
How does "quem" work, here?
A secondary point: Shouldn't future-perfect, "potuero", be completed before the future, "ornabo", can be invoked? Here, they will occur together, inevitably?