We already accept the
-Z- form, along with the related words
reutilized,
reutilizing and
reutilization.
The
-S- versions are given in a few dictionaries - Collins and the online Oxford, as well as Wiktionary - sometimes labeled as British variants. In fact it looks like the
-Z- versions may be the more frequently used, in Britain as well as in the US. Still, the
-S- forms are sometimes used. An example is from a Reuters report from November 2021:
"Relevant data related to pipelines, facilities and wells will also be shared to evaluate potential reutilisation of existing infrastructure for transport and storage in selected locations," Petronas said.
I'll add
reutilise,
reutilised,
reutilising and
reutilisation as rare words..