It will not be very simple...
Your score variable is a HUD variable displayed on your HUD. And because it is displayed as four (0-9) digits, in the code, you have to access via
Code:
LDA myScore ;; to read/load the value corresponding to the units
Code:
LDA myScore+1 ;; to read/load the value corresponding to the tenths
Code:
LDA myScore+2 ;; to read/load the value corresponding to the hundreds
And :
Code:
LDA myScore+3 ;; to read/load the value corresponding to the thousands
So if you use another HUD variable, you might need to display it as 4 digits, too (or mabe use 4 differents variables?)
In defintiive, when warping (or checkpoint), the code would be like:
Code:
LDA myScore
STA myScoreSave
LDA myScore+1
STA myScoreSave+1
LDA myScore+2
STA myScoreSave+2
LDA myScore+3
STA myScoreSave+3
And on losing life, it would be (the opposite):
Code:
LDA myScoreSave
STA myScore
LDA myScoreSave+1
STA myScore+1
LDA myScoreSave+2
STA myScore+2
LDA myScoreSave+3
STA myScore+3