The USEF doesn’t rate anything under 3’ (except age group Eq and Ponies) so the rules and definitions of eligibility and cross entries will depend on whatever organization is offering points in those 2’ and cross rails divisions when and if offered at USEF shows.
The USEF umbrella of rules regarding horse welfare, standards and conduct do apply, just not specifics of unrated divisions that are not Nationally rated. Usually these can be found in the prize list for that particular show and in that organizations rule book. Most are online these days. IIRC you do need to be a USEF member or sign an affidavit to show in a USEF show even in non USEF rated divisions and classes.
Ticketed warm ups are also not under USEF or Zone division rules since they are not judged rounds regardless of height or rating. It’s up to show management to even offer them and that depends on where you are located. Many areas you don’t see them as those shows offer judged schooling classes or red/blue only rounds. No points but they can charge you more then an unjudged ticketed warm up.