Simply insert a FILLIN field in the SEQ field to solicit the first number. For example:
{SEQ ID \r {FILLIN "First ID No." \d {SEQ ID \c}}}
Each subsequent SEQ field would simply be coded as:
{SEQ ID \n}
When you open the document, press Ctrl-A, followed by F9 to trigger the FILLIN prompt (which will default to the last number that was input). Insert the new number and press OK. All the numbers will be updated. No macros required.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]