There doesn't appear to be any way (except through SQL) to manage the length of history in Change Log Entries. After some research, it looks like a utility used to exist but is no longer available (why?!?!).
I wasn't able to find anything useful beyond this.
Being a novice administrator of BC on-premises, I'm at a standstill on this one (except to do it manually with SQL). I try to avoid involving our VAR for multiple reasons.
Thank you!