Can't say if your crate motor has a short nosed crank...did you buy it remaned from Mazda? If so I highly doubt it is a short nose.
If it is a short nose, you can change the timing belt without removing the bolt. You just can't change the front crank seal. Actually having the long nosed crank makes the timing belt change harder.
FWIW, I have changed the timing belt 2 times on my "old" '90 and 1 time on the "new" '90. Both have short nosed cranks and I have never found a problem.
I would advise changing the bolt and key if you do remove the bolt and generally follow the procedure at:
http://www.miata.net/garage/timingbelt.html
Also, the additional information on the short nosed crank at
http://www.miata.net/garage/crankshaft.html is good to use to evaluate your situation. I do think the recommendations about not using the bolt to rotate the engine are rather severe, however.
It's really not that big of a deal...