You can always put fields ( or merge fields ) on top of the button.
Depending on the look you want, you can even make the field, the button. (You can use the effect options for giving a field an appearance similar to a rectangular button.)
To make a field a button, simply select the field in layout mode and use button setup... to select the action to be performed when the field is clicked. (You'll probably want to take the field out of the tab order so users can't tab into the field or use Field/Control | Behavior to prevent entering the field.
The button's label must be entered on creation and cannot be edited?
The button's label can be edited using the Text tool.
I would first try what comment said. The text tool is the capital letter "T" button in FM10 (I think it was an "A" in FM9). Once you have made all your buttons, go into layout mode, click on the T (or A) and then on the buttons. It will allow you to change the text on the button, but keep whatever functionality you set when the button was added.