Can I remove some data from immutable table without leaving a trace

@Bryan_H @SruthiA @VValdar any comments?

I'm not sure "rollback to AHM" is actually a thing. Also, how exactly would you stop the AHM from advancing?

You can also drop or truncate an immutable table, it only deny update / delete operations.
So you can perfectly create a classic table, insert data from immutable, change whatever you want in the classic, truncate the immutable and move back the data.
It's extra work and requires more privileges (create & truncate table), but still doable.

You can stop advancing AHM in several ways - shutdown node, special database parameters, or using undocumented functions.
Though rollback to AHM it is not needed, immutable table really prevent only delete and update. As been correctly pointed out, you can drop or truncate whole table, or drop partitions.
Immutable table is not designed to prevent any changes to data.
Immutable table is a nice safeguard against accidental data loss, definitely very useful feature.