Thank you. Never heard of the cigar ash trick. Fortunately the few I have that are burned through are low quality/low price knock around pipes and probably not worth the effort.Nothing at all wrong with that practice. Alternatively, you can always spoon out a partially smoked bowl and stuff your excess in mid-smoke. As long as you don’t have too big a layer of ash between the two, it will be fine. And even if you do, that’s what a tamper and spoon are for. I wouldn’t overthink it.
As far as chamber holes, burn throughs, and other irregularities, the traditional practice is to fill them with a paste of water and cigar ash. As long as you don’t later dig the bowl like a strip miner, that usually sets up pretty good as a respectable insulating cake alternative for those areas. But use cigar ash; for whatever reason, other tobacco ashes are not as effective.