"I got the access contribution applied to 2021 after the W2 was generated"
Really? Or is what happened is that your employer withdrew the excess from 2020 and chose to recontribute it for 2021. This would be possible if your employer should have known that the employer contribution for 2020 was not valid and petitioned the HSA custodian to make the change.
That being so, then your employer should issue you a corrected W-2...the only issue with what you are suggesting is if you change your W-2 entry, and the IRS looks at your W-2 before your employer sends a copy of the corrected W-2 to the IRS - this sort of things triggers letters from the IRS. Or worse, the employer "corrects" something differently than what you expected.
The safer plan would be to file an extension, then wait for the W-2 to file. Note that the extension is an extension to file the paperwork, not pay the tax due. If you are expecting a refund, then it won't matter.
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