Hi Hugh,
Thank again for your feedbacks, for instance, if I simply over-write the posterior distributions, I would not be representative of what the sampler has explored during its run. I didn’t know of effect handlers and how to use them, thank you for pointing this to me! It could have work if the site values could be fixed stochastically with a distribution (the do handler set the prior distribution for a parameter from what I understood, and the condition set a site to a given value).
If found a way around in this thread where the definition of a custom sampling for each site is achievable using HMCGibbs. And this seems to work!