I noticed my new Victron IP65 charger was only putting out 14.2v during the absorption phase while charging my Ionic 12v 100aH battery. I had seen the Ionic website indicating their batteries should be charged at 14.6v, although I have charged it a few times to 100% with the 14.2v level and can't really tell if anything was different. The Victron will let me set up a custom charge profile which I can change the output to 14.6v for the charge phase. Has anybody set up a custom profile with their charger?

Nope.  Though, as long as it charges fully, I wouldn't worry about it.  Theoretically, a lower voltage will extend the batteries life, by introducing less heat.  But go too low, and it won't charge fully, or possibly even at all.  LiFePo4 batteries should charge between 13.8v to 14.7v.  14.6 is on the upper end of that range, so while still safe, a little higher than I'd want.  14.2 is right in the middle, so in theory it would be a better voltage as you'll generate less heat and extend the life of the battery, while ensuring it still gets fully charged.  

 

So if I did have a charger with a custom profile option, I'd probably set mine to 14.2v.  

I have the same charger and I’ve never considered changing it for the reasons @Bankc has already mentioned.  I’ve never needed to charge my batteries quickly.  They already recharge must faster than I do.