"existing format" is correct and usable in written English.
You can use it to refer to a particular format or style that already exists. For example: The existing format of the document needs to be updated in order to meet current standards.
"Accordingly, disc compatibility issues with new and existing format discs are possible.
The good news for the I.T.F. is that even with the existing format, Federer sounds readier.
Recognising that the existing format of British photography magazines was becoming tired he planned to merge existing Observer photographers with a new breed of British photojournalism.
It is also easy to import files from just about any existing format — music CD's, for example — and transfer them to the player.
The Wi-Fi industry plans to introduce a new security design next week that it says will solve the most critical flaws in the existing format.
If something is described as "new" or "the new [insert name of existing format or platform here]", there is the conveyance of a commendable sense of modernity; a feeling of momentum propelling us all forward.
Carrey's career slotted into existing formats and helped to revitalize them; Kaufman's career broke existing formats and created new ones.
"There are too many constraints to paint within existing formats," she said.
NBC has been aggressive in finding what might be called wrinkles in existing formats; its "Average Joe" and "For Love or Money" are clearly spins on "The Bachelor".
To qualify as an HD set, a television must be capable of displaying both 1080i and 720p signals, as well as existing formats.But then things get more confusing.
"The BBC's pursuit of audience share regardless of distinctiveness or innovation has been evident where the BBC has rushed to commission or produce almost identical programmes to those by ITV... we can see no obvious justification for the BBC commissioning existing formats such as The Voice for the UK audience," ITV said.
