The easiest method is to find a motif(full screen pack) and install it in the data folder. Fonts would go in the font folder, maybe... the readme will usually tell you where to put them.
To just change the life bars you would download the bar set and save the files in the data folder.
You then open up system.def and alter this line.
CODE
fight = bars\fight.def ;Fight definition filename
The name and area would be changed if necessary.
Same for hitsparks, but with it you replace FightFX.air and.sff
No need to alter anything in the system.def for this one.