Correct. If you restrict access to only one IP address, alternate IP addresses will not be able to access webmail (through cPanel) - in such cases as when you travel.If only to allow one IP address to access cPanel, I am unable to access webmail (at my domain) from different IP locations (when I travel).
I'm not sure exactly what you want to change/alter the setting to. However, following the guide lines provided in cPanel's article, if you'd like to remove the IP restriction from webmail, you'll have to do so in WHM's Host Access Control. You'd simply need to add a rule such as the following:How to change setting for webmail in cPanel?
webmaild : all : allow