I have been subject to the AMT since I’ve been married. My understanding is that under the AMT, my charitable donations are not deductible. If I find myself no longer subject the the AMT, can I c

You can always claim charitable contributions.  It's just that they are added back to your income when AMT is calculated so there's no net change in your overall tax due or refund..  If you are not paying AMT, the deduction reduces your regular income tax owed or increases your refund, up to the point where they are large enough to begin causing you AMT again.  You cannot enter charitable contributions from prior years though, just because you paid AMT in prior years..  In years when you pay AMT, you were still "allowed" the deduction, you just didn't benefit from it.