To merge such files, you could use
copy /V A.bin /B + B.bin /B C.bin /B
A.bin is file 1
B.bin is file 2
C.bin is target
But maybe mtkflash requires both files seperate so you wouldn't need to merge them anyway.
mtkflash is available for DOS nd windows, by the way.
But make sure you alway read and follow the instruction carefully!