you can exclude a certain GPU device from running a certain application of a certain project with cc_config, but be wary of what Van Zimmerman said above.
Either way, here's how you do it.
The cc_config.xml file is located in your boinc data directory (not in the project directory). It will most likely already exist. Back it up just in case.
You need to add <exclude_gpu> tags for every combinations of device+app that you want to exclude. You can add multiple of them. They go inside the <options> tag, so you can add them in the end of the file, just before the closing tag </options>
Assuming GT 710 is device 1 (and GTX 1070Ti is device 0), here's how you exclude GFN22
and here's how you exclude AP27
You can look up the names of applications to put in tha <app> tags here
You can also not specify the app tag to remove the device from running PG completely. There's another option to exclude the device from running any BOINC at all, look into <ignore_nvidia_dev> in the help page I linked in the beginning.
You have to restart BOINC client for the changes in exclusions to take effect. You can either do it by quitting BOINC manager while confirming quitting the client too (stopping the computation), which is a checkbox not enabled there by default... but it's also on a message box that has a "don't ask me again", so if you don't recieve it and you don't want to dig around in the interface to make it ask it again, it might be easier to just reboot the PC.