Custom characters in hp50p

[Helix]

You can put your modified font in the stack with the command FONT->. Then you can store it in a variable.
You can load a font with the command ->FONT.

To load automatically a font after ON-F3, create the following program in the HOME directory, named STARTUP :
<< 2:myfont RCL ->FONT >>
(in this example, myfont is stored in port 2)

You can do the same thing with the minifont, using the commands MINIFONT-> and ->MINIFONT.
To modify a minifont, you need an additional tool. You will find several minifont editors here:
http://www.hpcalc.org/hp49/utils/fonts/
I've used MFED, very simple and effective.

I hope this answers your questions.