HrastProgrammer describes this as follows.
"The idea of morphing filters is ... Instead of modulating individual Frequency/Q/Gain (which requires recalculating all internal filter parameters = CPU expensive) you set two predefined positions: Start (Filter Type/Frequency/Q/Gain) and End (Morph Type/Frequency/Q/Gain). Then you use modulation matrices to interpolate between those two positions. As a result, you can also morph between two completely different filter types (for example, between LPF and HPF etc.) which isn't possible with other filters (although you can use two filters and crossfade between them, of course)."
Morph can be placed before Filters A & B, or after the filters, and this is done by left clicking on Osc/Main tab to get to the hidden page then click on the Morph button near the bottom left of Tranzistow GUI. Morph/Pre means morphing will be placed Before the A/B filters, whereas Morph/Post sets them After the filters.