I have worked with the grid and have successfully been able to change the update/cancel button text/icon for inline editing using the code below.

commands.Edit().Text(" ").IconClass("fa glyphcolor fa-edit").CancelText(" ").CancelIconClass("fa fa-times").UpdateText(" ").UpdateIconClass("fa fa-check");

For the TreeList the IconClass, CancelText, CancelIconClass UpdateText or UpdateIconClass are not exposed functions.  Currently using JQuery and CSS you can workaround this but I would be nice if the TreeList exposed this functionality as the grid does.