Adapt a programme designed for XP to run on Windows 8

We have a programme originally developed for Windows XP and Vista 32 bit.

When Windows 7 and 64 bit operating systems came out and demanded enforced driver signature, we developed an installation patch that loaded prior to Windows 7, simulating pressing the F key and automating the "disable driver enforcement" option, then allowing the machine to boot up in the normal manner, thus enabling the drivers to be loaded without signing.

We now need to adapt this programme to run on Windows 8.

Unfortunately the original designer is not around any more, but we have all the source codes.

It is absolutely vital that none of the programme functionality is affected by the adaption to Windows 8

This is a very niche piece of software with very low sales, only about 250 a year, so a complete redesign is not viable.

Is there anyone who believes they can do this at reasonable cost?

We would ask anyone to sign an NDA for obvious reasons.