Many thanks folks; some interesting comments.
True, reduced thrust can give lower VMCG. However, on our engines, if you advance the T/L's after THR HLD you can achieve full 26K even if 22k was enterd via the FMC. Doing this might infringe the V1 v VMCG relationship. Doddgy? but there is no notice not to do so.
About the effect at CLB power. I thought that as the preset thrust is reduced, by whatever means, the CLB is automatically preset to either full, 1 or 2 to match the takeoff thrust setting. Thus at 22k and assumed temp the CLB would likely be CLB 2. Further I thought the FMC would allow the assumed temp to reduce thrust by either 25% or the pre calculated CLB setting. Thus I wonder why at climb power setting there could be a thrust increase. That would suggest that the reduction in takeoff thrust had been too great. It is true that the selected derate and assumed temp are entered first and the selected CLB follows, but surely the FMC would obey the max reduction rules?
What am I missing?