Let $(X, \wh X)$ be a pair of Borel standard processes on a Lusin
space $E$ that are in weak duality with respect to some
$\sigma$-finite measure $m$ that has full support on $E$. Let $F$ be
a finely closed subset of $E$. In this paper, we obtain the
characterization of a L\'evy system of the time changed process of $X$
by a positive continuous additive functional (PCAF in abbreviation) of
$X$ having support $F$, under the assumption that every $m$-semipolar
set of $X$ is $m$-polar for $X$. The characterization of the L\'evy
system is in terms of Feller measures, which are intrinsic quantities
for the part process of $X$ killed upon leaving $E\setminus F$. Along
the way, various relations between the entrance law, exit system,
Feller measures and the distribution of the starting and ending point
of excursions of $X$ away from $F$ are studied. We also show that the
time changed process of $X$ is a special standard process having a
weak dual and that the $\mu$-semipolar set of $Y$ is $\mu$-polar for
$Y$, where $\mu$ is the Revuz measure for the PCAF used in the time
change.