spice modelling of variable resistance
So to summarize:


if a precise curve of the resistor vs time doesn't matter .step param, which is supported in PSpice, is a good way. Actually you can remain ignorant of the SPICE dot command syntax in PSpice, because parametric sweeps can be configured entirely via GUI menus (Simulation Settings > Primary Sweep) as explained in this tutorial: http://m.eet.com/media/1179065/chapter (see p. 69)
for a curve vs time: SPICE3 behavioral expressions. I'm not sure exactly what PSpice supports in this regard... It seems the preferred way of doing this in PSpice is to use its Analog Behavioral Modeling (ABM) extension, which allows abstract components that can use TIME as a variable; see http://www.nordcad.dk/download/Forum/PSpice/abm.pdf for an overview. At least for this problem, it seems ABM is actually the same thing as a SPICE3 behavioral expression, with a (PSpice) syntax like R1 1 0 VALUE={10 + 0.01 * TIME}.