I would appreciate having more samples. 1024?
You can use up to 4,000 samples in instrument mode. They can be assigned to 255 instruments at max. Since all pattern fields are 8-Bit, there is no way to encode a higher instrument number than 255 in the pattern.
could it be possible to expand the pattern length more that 1024?
Possibly. The problem is that the internal communication between parts of the program relies on some variables (like the current row indicator) having a maximum width of
n bits, where
n is 10 for the pattern row, I think.