Yet another changing-my-name-server's-ISP question

[gschmid at notes.cc.sunysb.edu]

I'm hosting about 40 domains on my name server,
and we will be switching ISPs shortly, so the
name server's IP will be changing.

If, for example my domains are:

domain1.com
domain1.net
domain1.org
domain2.com
domain3.com
domain4.com
etc...

and the name server for all of them is
ns1.sub.domain1.com, how many
registrar-level changes do I need to make
assuming the FQDN of the name server
stays the same and only the IP is changing?

Would there be one glue record in the .com zone
for "ns1.sub.domain1.com" which would cover
all 40 domains that I need to change?

May I assume that the .net & .org zones don't have
a glue record for my .net & .org domains if
the NS is under .com?

Also, how does one get a glue record changed?
Can I just make a name server change with my
domain1.com registrar?

I just need to know whether I need to
make 40 changes, 1 change, or some other number.

TIA.