You must remove the lift cover to replace the draft control plunger.
Due to corrosion, it is usually not possible to remove the pin connecting the plunger to the draft control fork so you will need to remove the plunger/fork as an assembly. This can be done after disconnecting the fork at the front and removing the draft control spring and plate.
If memory serves, you will need to remove the touch control lever shaft, which will require removing the cylinder from the lift cover to reinstall.
I have had no luck at all having CNH dealers adjust the internal linkage as nearly none of them still have the proper tools necessary to do so. Note: this is not to say that they will tell you that they cannot properly adjust the linkage. Rather, some (many, most, all?) simply guess at the settings, and tell you that things are fine.
I strongly advise performing the linkage admustments yourself using the alternative procedures (special tools not needed) in the I&T manual.