Frequency response of FIR (MTI delay line canceller) with non constant period
If you mean that you want a time-varying delay then the whole system becomes time-varying, which means that there is no such thing as a frequency response in the conventional sense. Only linear time-invariant systems can be described by a frequency response. There are of course ways to describe time-varying systems, but the question is what it exactly is that you expect from such a description of the system. What you've done in your example is subtract two delayed signals from the original signal, which is in fact a time-invariant system. In sum, what you're looking for (a frequency response description of a system with a time-varying delay) does not exist.