That's fine. The polarizing filters also have a rotary thread on the front where the filter plug-in system can be attached. 

As K&F Concept ND2-ND400 filters adjusts the amount of light that can pass through with polarizing glass, a colour cast can't be avoided for all the variable ND filters on the market. However, K&F Concept variable ND filters are made by the best coating technology, which reduces the effect of the polarizing film on image color. *Based on our professional test, the colour cast of K&F Concept ND2-ND400 filters is around 290k while the industry standard is 500k. 

I don't see why not, remember that the filter goes on the lens, not on the camera. 

hello the K&F Concept Slim UV Filter + Slim Circular Polarizing Filter (CPL) + Neutral Density Filter + Slim FLD does not work for work for the solar eclipse 

If you polarizing filter is square and size is 100X100mm, the hold is okay for you