Hello Serhan and Douglas,
Yes my question was ultimately more general :
given the (say) 3-components vector example, {f[x,y,z],g[x,y,z],h[x,y,z]}, and the three sets of rules, rulef={x->uf,y->vf,z->wf}, ruleg={x->ug,y->vg,z->wg}, ruleh={x->uh,y->vh,z->wh},
to apply rulef to f[x,y,z], ruleg to g[x,y,z] and ruleh to h[x,y,z] in a single and concise way.
MapThread (apparently not Inner) does the job (see Frank's post above) :
MapThread[ReplaceAll, {{f[x, y, z], g[x, y, z], h[x, y, z]}, {{x -> uf, y -> vf, z -> wf}, {x -> ug, y -> vg, z -> wg}, {x -> uh, y -> vh, z -> wh}}}]
Answer : {f[uf, vf, wf], g[ug, vg, wg], h[uh, vh, wh]}
Regards