Hi what up,
You cannot change the file extension in Lightroom. File format would remain raw however, you can change the file name in Lightroom.
Refer this article : File rename options | Adobe Photoshop Lightroom CC tutorials
You can't change the file Extension and expect any program to properly read the file. The only thing you can do is convert the RAW files to the Adobe DNG format.
You could export them as TIF or PSD files and have the same high resolution. But they would no longer be raw files. What file extension does the client want?
Can you be more specific about what extension your files have, now, and what extension the client wants?
Also, what do you mean by hirez files?
Is this a situation where your client wants JPGs or TIF copies from your raw files? If so then you don't make JPGs or TIFs by renaming the raw files to have an extension of "JPG" or "TIF", instead you create these new files by using File / Export after selecting the raw files and choosing the JPG or TIF file format type in the Export panel options, then clicking Export.
The second part of your subject seems missing from your initial question. You say rename raw files then color correct. Normally what you'd do is make corrections, color correction, or whatever else, to the raw files in LR, then use File / Export to create corrected copies in JPG or TIF format.
No workflow I know of involves renaming extensions of raw files then doing color correction.