Just be careful not to reduce the limit on cards while AUs are on it. While they may not notice, if they do they might be peeved if they paid $X for a $20,000 limit for 3 months, and ended up getting a $20,000 limit on their credit report for one month and a $1,000 limit for the remaining two months.
And if they're peeved and complain to the piggybacking company, then they in turn will not be happy with you.
@Padonak, up thread there's a discussion about a lifetime limit on the number of AUs a Barclays card can have. I don't recall the number offhand, and IIRC it varied slightly between reports, but it's a decently large number on the order of dozens. Presumably
@Reddart67 has kept track of how many AUs they've added and are nearing the limit.
The only solution I know of is to apply for a new Barclays card and season it, then shift CL over with care.