d4 to d7 are protection for Q4 to Q7 incase a DC voltage is applied to the output of the power supply.
D8 protects the MC1466 if the pass transistors (Q4 to Q7) fail when there is short circuit on the output.
I was planning to use r4 value changed to 0.01r as a current sense resistor and measuring the voltage dropped across it to drive a digital current meter but it doesn't look like it will work with d8 in place.
That will change the current limiting setpoint and adjustment range. Changing R4 from 0.05R to 0.01R means the max limit setting goes from 4A to 20A. Setting it to 20A will result in smoke. D8 wouldn't be a problem for using R4 as a measuring shunt since the voltage across R4 should always be much less than 0.7V
Instead of changing R4, you could put an appropriate trimmer pot across it and scale the voltage that way.