  The London penetration depth, $\lambda (T)$ was measured in single crystals
of Ce$_{1-x}R_x$CoIn$_5$, $R$=La, Nd and Yb down to 50~mK ($T_c/T \sim$50)
using a tunnel-diode resonator. In the cleanest samples $\Delta \lambda (T)$ is
best described by the power law, $\Delta \lambda (T) \propto T^{n}$, with $n
\sim 1$, consistent with line nodes. Substitutions of Ce with La, Nd and Yb
lead to similar monotonic suppressions of $T_c$, however the effects on $\Delta
\lambda(T)$ differ. While La and Nd doping results in an increase of the
exponent to $n \sim 2$, as expected for a dirty nodal superconductor, Yb doping
leads to $n > 3$, inconsistent with nodes, suggesting a change from nodal to
nodeless superconductivity where Fermi surface topology changes were reported,
implying that the nodal structure and Fermi surface topology are closely
linked.
