I've checked a few sources on this matter, and I've tried doing this on my own. Here's the scoop.
There's a VI you can download to do this, and it modifies the windows registry to change the .daq file that MAX is looking for. Two drawbacks:
1) It's done with 6i VIs that don't exist in 5.1, and you don't have 6i.
2) You must restart MAX (physically start it) for the change to take affect.
If you leave MAX set up to look at the default niconfig.daq file and then make your .daq files with different filenames, you can do the same in 5.1 by just copying your .daq to niconfig.daq, but in this case, you'd STILL have to run MAX for it to take effect.
Therefore, after copying the .daq file, you'd have to programmatically open MAX (and then either close it, or j
ust leave it open). That would do what you want.
Hope that helps.
Mark