He did. Sort of.
You can read about the Siege of Ravenna in Procopius here. To sum up the events:
- Things got dire for the Goths inside
- Diplomats from Justinian arrived and offered the Goths the term of keeping half the treasury and territory north of the Po river, with the rest going to Justinian and the Goths becoming subjects to which the Gothic king Vittigis agreed.
- Belisarius did not like those terms and refused to sign off on them, arousing suspicion from both the Goths and other Roman commanders (can you say insubordination?)
- All the other Roman commanders wanted to follow Justinian's terms, but Belisarius said if he could achieve a quicker and more complete victory he should. The other commanders didn't think more could be done and Belisarius asked them to put that in writing.
- Goths were worried Justinian would resettle them in Byzantium and so asked Belisarius to be Emperor of the West.
- Belisarius met the other Roman commanders and said he had a way to get complete victory and they agreed he should do it. He then sent away the generals most likely to be against him to other parts of the country.
- Belisarius pretend to accept the position of Emperor of the West and thereby entered Ravenna and captured Vittigis and the Goths. The capture of Ravenna caused most Goths to submit.
- Persia was preparing to launch another war with the Romans so Justinan transfers Belisarius to the Eastern theatre against the Persians. The Goths begged Belisarius to stay but he went.
So, Belisarius did "accept" the crown, after he of his own rejected Justinian's terms for the Goths surrender if I might add. I mean sure, he faked it to capture Ravenna, but isn't that basically the same thing as what you're suggesting?
He was just immediately transferred to fight the Persians after.