Does anyone know how to program a COP410L?

Hello,

I have a solarium ("tan light"?? - don't exactly know the name in english...) from PHILIPPS I use to make my PCBs; it is almost 12 years old.

It has a 2 digit LED display and only indicates minutes.

I need to have it indicating seconds.

So I opened it and found a COP410L microcontroller inside.

I have two solutions:
1) I replace this µc by a PIC (pins are different so I will need to adapt quite a lot...)
2) I reprogram the existing µc, yes, but how...

I found the data-sheet (Nation Semi-Condutor) but cannot understand the way they porgrammed this chip.

Does somebody know how to program this "old" µc in a simple way or am I waisting my time on this solution?