How to redirect file I/O operations of a process to memory or a different file?

Question

Let's say I have a file named file.txt and a running process with PID 12345 which sometimes reads and sometimes writes to that file.

1. Is there any way I can fool the process with PID 12345 to read or write to memory (allocated by another process) every time it tries to read or write to file.txt?

2. Is there any way I can fool the process to read and write to a different file (like file2.txt)?

On Windows.

Same question for Unix/Linux.