Custom TFS Check-In Policy: "Uncheck" a checked pending change during evaluation

Question

I have an Check-In-Policy extension for VS2017 (using TFS 2017) that checks if the pending check-in contains files matching a given regex.
In case matching files are contained in CheckedPendingChanges the Evaluate method returns the PolicyFailure to avoid checking in these files.

[Serializable]
public class FileWarningPolicy : PolicyBase
{
   // ...

   public override PolicyFailure[] Evaluate()
   {
        Regex regex = new Regex(Pattern, RegexOptions.Compiled | RegexOptions.IgnoreCase);
        if (PendingCheckin.Policies.EvaluationState != PolicyEvaluationState.Evaluated) return new PolicyFailure[0];                
        var matchingFiles = from change in PendingCheckin.PendingChanges.CheckedPendingChanges                                   
                            where change.IsEdit && regex.IsMatch(change.ServerItem)
                            select change;               

        return matchingFiles.Any()
               ? new [] { new PolicyFailure("some error message", this)
               : new PolicyFailure[0];

    }
}

This works fine. But it would be far more comfortable if I were able to simply "uncheck" these files to exclude them from the current check-in but not abort the whole check-in.

Through the PendingCheckin.PendingChanges property I have access to the current Workspace which has a lot of methods to download, check-in, check-out, shelve etc. the repository items, but nothing to only uncheck/exclude them from the checked pending changes (only to add an exclude entry to .tfignore, which is not what I want).

Is there a way to achieve this?