I have a timer set up with fast PWM and ICR1 = 0x1FF;

Assuming that value is a uint16_t in the range 0-511 do these both do the same thing?

// Version A
OCR1A = value;

// Version B                                            
OCR1AL = value;                                                                                                    
value = value>>8;                                                                                                   
OCR1AH = value;

Ok, to answer my own question, these two bit of code create the same two assembler instructions

// Version A
OCR1A = value;

// Version B
OCR1AH = value>>8;
OCR1AL = value;