This is a feature that has had me scratching my head for years. It looks like they were going to change something, but never got around to it.
The software will always look for the fig_pref.db file in one place and one place only. There's no tab to select any other file.
Now here's what is really odd. Look under "Documents and settings/all users/application data/autocad ldt*/data/survey". There's the file. Also note that under that there are folders "Company Set" and"NCS set". There are survey folders under those headings that contain another fig_pref.db file that is different in each location.
The only work around that I have come up with is to create a new subfolder for your company standards and copy your current fig_pref.db file there so you will always have it.
Then open a new drawing and change the fig_pref.db file to your clients settings. Now go back to "Document and Settings", make a subfolder with their name on it and copy the modified file under "Survey" to that folder.
All new drawings that you start will now open with the clients set-up.
When you are through with his stuff, copy your company standard fig_pref.db file back under "DATA" to overwrite that file to re-set your company standards.
Each time you are going to use a different set-up you must remember tocopy the correct fig_pref.db file under the "Data" folder.
That can get VERY confusing and you WILL mess up every now and then, but this is the only way I can see to do what you want.
Ther has to be a better way, but I have not found it yet, and I have been using AutoCad since 1988.
(AutoCad needs to look at this. Other survey and civil engineering software allows you to greate multiple figure prefix libraries. I gues they don't look at this because they say only 10% of the users are using this feature. Poppycock!!)