How can I isolate voltage reference from ICSPCLK programmer output
I don't think there's a good way to do it. My first suggestion would be to just add a jumper in front of the LM282:







simulate this circuit &ndash; Schematic created using CircuitLab

The jumper (or DIP-switch) should be closed during normal operations and open when programming.

If you absolutely cannot live with this requirement for manual intervention, you may throw in an op amp to avoid that node altogether:







simulate this circuit

This way your programmer will "fight" against the op-amp, but if the resistance (R2) is high enough, the programmer would "win". During normal operations, the op-amp just buffers the voltage reference. If you go that way, pick an op-amp that accepts inputs and outputs close to the rails - Rail-to-rail I/O.