Manually the Preset can only be changed in the Manual and handwheel modes so can't edit the active preset while the machine is running.
But here are some ways around it.
1- program can automatically change any preset other than 0 using functions and variables.
2- change it offline (ie connect through TNCremoNT change file send it back to control.)
3- goto programming and editing mode, copy existing preset table to another name make changes. Copy file back to TNC:\preset.pr.
maybe some other ways too
I would suspect methods 2 and 3 have ka-bloomy written all over them.
1 wrong figure and you're looking at a box of broken bits where once you had tools and a fixture.
2 alternatives occur to me
Insert a M01 optional stop just before the pallet switch, this will let you safely put the machine into manual and edit the preset table, then do a safe restart in slow motion to check you have'nt done anything stupid such as put in Z-200 for the Z height when it should be Z+200
Or
If you use a program for each pallet, then start the program something like this
0 BEGIN PGM Pallet 1 MM
1 CYCL DEF 247 DATUM SETTING ~
Q339=+1 ;DATUM NUMBER
2 CYCL DEF 7.0 DATUM SHIFT
3 CYCL DEF 7.1 X+0
4 CYCL DEF 7.2 Y+0
5 CYCL DEF 7.3 Z+0
6 ...... etc etc
This will allow you to move the datum while Pallet 2 program is running
Assuming of course you run something like
0 BEGIN PGM PALLET_MAIN MM
1 LBL "LOOP"
2 CALL PGM Pallet 1
3 CALL PGM Pallet 2
4 CALL LBL "LOOP" REP 5000
5 END PGM PALLET_MAIN MM
Boris
<<is suffering from Brain fade caused by trying to machine a hydraulic actuator 250mm long on a 4 axis VMC