@Stang is this the style of the edit you wanted to make prior the the whitelisting?
https://www.wikidata.org/w/index.php?title=Q109622820&type=revision&diff=1530637309&oldid=1530636710

@Xaosflux, yes.

Did a quick test on beta cluster, found something weird (not that relevant to this task though)

1. Add \blinktr\.ee\b in global Spam_blacklist - everything looks great, I got trapped when adding link https://linktr.ee/JasonSeah
2. Add another entry \blinktr\.tv\b to global Spam_blacklist, seems I did not get trapped anymore...

Is there something wrong with my operation?

Could this be because edit summaries are checked for spam, as mentioned in T15599#173812? Removed content can appear in edit summaries in the Wikidata user interface (and other scripts and tools) and there is usually no way to save with a different summary.

(if this is the reason, it should be possible to restore a revision from before the addition, if it was not there from the first revision)

For reference, edit summaries are indeed conditionally checked for spam:

// HACK: treat the edit summary as a link if it contains anything
// that looks like it could be a URL or e-mail address.
if ( preg_match( '/\S(\.[^\s\d]{2,}|[\/@]\S)/', $summary ) ) {
	$links[] = $summary;
}

For Wikidata, this is unfortunate because when you remove a piece of data ("by hand"), it is usually included in the edit summary.
Paradoxically, when the domain is put on the blacklist meanwhile, the only one blocked by the filter is the cleaner, not the spammer.