Add border to all buttons after v1.2.0

In ionic 1.2.0 the border of buttons was removed. This was done by setting border-color always to to transparent in _mixins.scss (see commit 21e54be).
Is there any way the border can be added again, without modifying this sass file (because it could be overwritten by an update)?
I thought about copying the mixin into my own style file, but this didn't work (probably because I can't overwrite the mixin between the first definition and the first use). Another way would be to overwrite the border-color attribute for all button styles that I use, but I thought there must be an easier way.