In addition to growing pages using VirtualAlloc, it's also possible to have the same memory pages mapped at different locations by using memory mapped 'files' (even when the backing file is just the paging file). This means that if your new block isn't contiguous, you can remap the existing memory without a copy.

However, system calls also have overhead (thanks Meltdown/Spectre mitigations), and you might not come ahead by avoiding memory copies.