1. Yes, Maryland allows filing separately after filing jointly on the federal return, but there are special instructions on page 3:
https://forms.marylandtaxes.gov/current_forms/resident_booklet.pdf
2. Since you are using the desktop version, TurboTax would flow to state correctly if you have the same filing status. For example, you would do a mock federal filing separately when completing the separate Maryland return. See instructions below:
3. No, Maryland TurboTax does not give you the option to change your filing status from what the federal return is.
If you have more questions about this, ask in the comment below.
https://ttlc.intuit.com/replies/3301995
