As Chris has noted, editing custom fields requires the Desktop client to use Administrator level access. In all versions (up to/including current v10.2) NP will still function - as it uses read-only data access - as long as you don’t do any of the following:
Any of the latter changes cause an alteration to the catalogue’s field table and causes NP to not be able to read the catalogue correctly**. The fix us simple. as soon as you’ve finished editing the custom fields and committed the changes in Portfolio, simply re-start NP (Win via NP OS service or on Mac via NP app Launcher).
** For a different but different reason, but to same effect, res-tarting Portfolio Server without then re-starting NP will cause the later to malfunction.
IIRC, you may be able to edit the predefined value lists of existing fields (without changing the overall field) and not upset NP, but to be safe I’d restart NP just in case.
Lest you wonder, Portfolio/NP offers no way to automate the NP restart based on Portfolio Server changes (though it’s a frequent feature request). So, you want to make sure that anyone with admin access to Portfolio knows of the edit actions that may necessitate an NP re-start.