Not so sure. If you grind out the cracks then clean, mix a small batch of CC resin and full. Tape thick smooth plastic over it to keep it in place until cured. Then blend into area. Fiberglass products tend to adhere to themselves pretty well in repairs. Will be some color variation but it's just so crazy it might work.
Worst case is to grind, clean, fill with epoxy, then smooth/blend and prime locally. Then hit area with some RubNBuff to blend back in, then add a little helpful "weathering" at that area....worth a shot anyway and sounds good on paper.
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Back to boots. If anyone else has suggestions or finds some that they can't use, quite a few folks here would love to pick them up.