  The study of exactly marginal deformations of superconformal field theories
is a topic that has received considerable attention due to their rich
properties. We investigate the $\mathcal{N}=2$ preserving exactly marginal
operators of 3d $S$-fold SCFTs. Two families of such theories are considered:
one is constructed by gauging the diagonal flavour symmetry of the $T(U(2))$
and $T(U(3))$ theories, and the other by gauging the diagonal flavour symmetry
of the $T^{[2,1^2]}_{[2,1^2]}(SU(4))$ theory. In both families, it is possible
to turn on a Chern--Simons level for each gauge group and to couple to each
theory various numbers of hypermultiplets. The detailed analysis of the exactly
marginal operators, along with the superconformal indices, allows us to
determine whether supersymmetry gets enhanced in the infrared and to deduce the
amount of supersymmetry of the corresponding SCFT.
