By top tube bag, you mean one that sits on top of the tube ? yes.
Depends on how thick the velcro fixing tabs are, and where they sit when you attach a bag to where the cable stop/braze on is.
The velcro should sit underneath the brake cable ok, you might get some contact but shouldn't be enough to really affect the brake operation.
You could be creative and use a biro pen outer as a sleeve and just wrap the velcro around that for a small top tube feeder/phone bag.
By top tube bag, you mean one that sits on top of the tube ? yes.
Depends on how thick the velcro fixing tabs are, and where they sit when you attach a bag to where the cable stop/braze on is.
The velcro should sit underneath the brake cable ok, you might get some contact but shouldn't be enough to really affect the brake operation.
You could be creative and use a biro pen outer as a sleeve and just wrap the velcro around that for a small top tube feeder/phone bag.