Yes I was reading that the other day, I think that's what I will do for now, would be nice to be able to change individual icons though.
Ps - you may want to change the ".svg" to .png in the guide linked.
While I'm thinking about aesthetics:
Is there anyway to have a roll over effect on the top options?
At present there is no way of telling if you are going to click Remove books, or the arrow to the right, Save to disc or the arrow to the right etc
This may cause issues with people clicking on the wrong icon, if a roll over colour change could be included, that would stop any mistakes (and you know how delete mistakes are prevalent at present)
If colour change is not possible, maybe more space between the options, or change it altogether to a right click on the icon for the extra options?
Just suggestions - the program is awesome "as is"