Is it possible to reserve a desired region of a given hard disk drive for placement of the pagefile.sys before enabling the page file on that drive?
Windows only allows you to choose the drive letter on which the paging file resides, you cannot select a sector offset or range.
That said, if by "desired region" you would accept "separate partition" then yes, you may select a specified region on a disk. You would need to create a valid partition in the desired region and assign the partition a drive letter in within Windows. Then you would select the new drive letter as the paging file location.