Replacing front gear cable without removing cable housing
I’ve never had any issues with only replacing the cable (they break from time to time). The important part is that the housing sits snuggly against the brifter so that you can hit the hole with the cable. If it does not you can lift the rubber grips and try to guide the cable into the housing.

Just make sure the cable end is not frayed when you remove it. It can get stuck and/or destroy the housing.