Actually, I never thought about the issue when attaching numerous xrefs at once. IMAGEATTACH only allows inserting (1) .tiff/.jpg at a time but XATTACH will allow numerous, this indeed could be problematic. 90% of what we do is based on IMAGEATTACH the other 10% is based on XATTACH. In that case changing the layer before insert would be ideal (in terms of length of script) I imagine a semi? simple foreach function to process each xref prior to insertion. I shall dig more into that one.
The methodologies needed are already provided above, and you'll need only work through the implicit tasks... In short, you can ultimately use the same reactor for both, as is demonstrated in my earlier linked post, using a COND statement.
In regards to multiple xrefs of the same name in different locations, from my understanding you can't have 1+ xrefs of the same name as Autocad will just use the previous definition.
Xref "Drawing1" has already been defined.
Using existing definition.
Try using Reference Manager.
Standards or the lack there of is a good point, this routine was brought up as more so a "forced" standardization. Previously the layer or the xref was just "Arch-Roof" or "Civil-Utilities" or worse I have seen "XREF" here. I'll have to look more into what universities or other public standards require in terms of naming.
In standards, the same rule(s) apply... Keep it simple... The more variations of what those reference name-dependent layers are, means more layers to manage within various Layer States, or where VISRETAIN == 1, etc., more management means less time catching the important design aspects that cost you even more time, etc. later in a project's design.
While perhaps simple, as compared to today's BIM, NCS, etc. standards, I would gladly take even "XREF" over a drawing where each-and-every-single reference has its own layer.
Also, for what it's worth... Universities are the last place you should look to gain wisdom, and they have little if any practical knowledge when it comes to real-world production value (my $0.02).
Cheers