Thank you @Mark_Bailey ! My rationale for wanting to switch from REML to ML is based in model selection protocol for R. Where one cannot compare the AIC values of two mixed effect models that differ in their fixed effect structures when using REML. The math underlying this goes over my head, but presumably the same comparison applies to comparisons of mixed effect models using REML in JMP? Or perhaps JMP automatically refits the model using ML to generate the AICc values to facilitate model comparisons. If such refitting is going on "under the hood" that'd be great to know!
Faraway (2006) Extending the linear model with R (p. 156):
"The reason is that REML estimates the random effects by considering linear combinations of the data that remove the fixed effects. If these fixed effects are changed, the likelihoods of the two models will not be directly comparable"