Under conventional wisdom, no, they can't. The certification deadline was Tuesday, 14 days of the election, by state law. Further, there's no apparatus I'm aware of by which they can rescind a vote that wasn't otherwise invalid (e.g. pressured illegally to vote a certain way), anyway. Even if they did rescind their votes, the state of Michigan would certify the results in lieu of a certification at the county level.
However, I mentioned before 'under conventional wisdom'. This isn't Law.SE, so I haven't gone into what relevant law might say. There are a number of lawsuits currently being attempted in order to stop or change the Wayne County certification process. Any one of them could result in a court ruling to re-do something, if a judge decides to take up the case (so far, I think all of some two dozen lawsuits by the Trump campaign or their supporters to overturn, stall, etc. the results of various voting processes have been either dropped or rejected by the courts).
To provide a bit of context, the two Republican members of the certification board were apparently advised by their legal counsel (according to local reporting) to vote to approve the certification 'under condition of an audit' being performed afterward. After they did so, the Michigan Secretary of State announced they did not consider that condition to be legally-binding, and so dismissed the notion. Because of that dismissal, the two Republican members of the certification board have signed sworn statements indicating they regret their prior vote in favor of certification, and wish to rescind said vote.
Whether said affidavits have any legal weight on the process is a matter for the courts to decide, if they so choose. If they do not, or if we reach a point where Donald Trump has conceded the race or where Joe Biden has been sworn in as the next President, then the argument will be moot. Even if they do, it's unlikely to effect a change at the scale needed to cause Biden to lose the state of Michigan.