It is not possible, no. If you need to dynamical and smoothly change the scrolling speed of a texture, the only solution is to do the panning via a blueprint, at least while you’re doing the rate adjustment. You can easily calculate the appropriate offset to add to match the material or blueprint controlled panning so the transition between the two doesn’t pop.
The trick is in your material have both a panning rate and a manual offset, uv = uv + frac(rate * time + offset). When you need to smoothly change the panning rate, use (current rate * (time - delta time) + offset) % 1.0 to get the current total offset, then set the rate to 0 and pan using only the offset value with offset = (offset + delta time * rate) % 1.0. When you want to go back to letting the material do the panning, set the materials rate again, and set the material’s offset to (rate * time) % 1.0 - offset.