Hi Greg...
There's almost always a way to do something in Pro/E... the problem is determining whether or not your SHOULD. Frank's right, there's certainly no easy way.
In the model you can use rel_model_name() to have the system return the name of the current model. For example, you can set a relation that says:
current_name = rel_model_name()
That relation will set the name of the current model to the variable "current_name". But this isn't what you asked. 
You can ALMOST do what you're trying to do with a mapkey. The problem occurs when you try to use a variable while renaming your datums. The system doesn't want to let you input a variable for the new name. It actively resists this. This means you have to build the name of the datum plane WITHOUT entering a variable name.
How in the world do you do this? You'd need to create a small trail file and re-run it using a mapkey. Most people use trail files in an attempt to recover lost work after a crash. This is virtually useless except for a few rare cases. However, trail files are great if you want to run a whole slew of commands at once and you don't (or can't) build them all into a mapkey.
Start Pro/E completely fresh. (Restart from a blank session). Start a brand new file (from a start part). Immediately edit the datum names. Input anything you want for the names... ie "test_front", "test_side", "test_top", etc. When you're done, save the file and exit Pro/E. Now go find the trail file created from that simple session you just ran. Open the file and look carefully for the lines where the names of the datums are added. Check specifically for "test_front", "test_side", and "test_top". These THREE lines are the important ones.
Also... there's a line in there somewhere when you NAMED your new file. That line will contain your model name. So now you have all information you need.
Here's the rub. You have a perfectly good file... all you need to do is substitute a new model name a few places and you'd be golden. BUT... you want to use this file over and over using a different model name each time. The easiest way to do this is with some type of script. It can be DOS, some kind of shell, or my favorite- PERL. If you have the patience to learn a quick bit of Perl, you can write a 10 line script which will replace the model name into the appropriate lines in your trail file.
In practice, you'd start a new part or assembly, give it a name... and then hit a button or mapkey. The mapkey would fire off the PERL script. The script would take your trail file and edit in the appropriate new model name and save it. Once the script executes, control goes back to the mapkey... which then opens the trail file and executes it.
All of this should happen in a fraction of a second... and all your datums would be renamed. Voila!
If you want me to help you create this system, I'd be happy to do it. I can help you with the scripting too if that would help. It's not EASY... but it is possible. You just have to have a little MacGyver in you!
Have a great holiday!!
-Brian
