The experimental results reported here demonstrate that weakly bound van der Waals complexes are not necessarily kinetically trapped in different isomeric forms in a supersonic expansion. We have recorded the laser-induced fluorescence spectra of the near T-shaped and linear He...ICl(X(1)Sigma(+),nu" = 0) complexes in the ICl B-X, 3-0 spectral region at varying distances along the expansion direction to monitor the populations of the two isomers as the local density, collision frequency, and temperature change. The ratio of the T-shaped to linear complex populations monotonically decreases with increasing downstream distances and thus lower ICl(X) rotational temperatures. Conversion from T-shaped to linear complexes is still observed at the furthest distances where a temperature of 0.57(8) K is measured.