The Swagger API does not support this, as far as I know.
These values may be set from the command line using VSEManager. The brief help for this tool is, below - the --update option is relevant to your question.
This command line tool is used for managing virtual service environments.
Syntax:
VSEManager options command [ ... command ]
where "options" may be one or more of the following:
--registry <name>
Used to set the name of the DevTest Registry to work through.
--vse <name>
Used to set the name of the virtual service environment to work with.
--username=<name>
Used to set the ID of the user to authenticate with when ACL is in use.
--password=<name>
Used to set the password for the user to authenticate with when ACL is
in use.
and where "command" may be one or more of the following:
--status [<vs-name> | all]
Used to print out the status of one or all virtual services in the
current environment.
--deploy <archive-file>
Used to deploy a new virtual service to the current environment. The
archive file must have a virtual service model as its primary asset.
--redeploy <archive-file>
Used to redeploy an existing virtual service to the current environment.
--update <vs-name> [--capacity <capacity>] [--thinkscale <scale>] [--grouptag <group tag>]
[--auto-restart [on|off]]
Used to update the capacity, think scale, group tag, auto-restart setting, or any
combination thereof for the named virtual service.
--remove <vs-name>
Used to remove the named virtual service from the current environment.
--start <vs-name>
Used to start the named virtual service in the current environment.
--set-exec-mode <vs-name> --mode <exec-mode>
Used to set the execution mode for the named virtual service in the
current environment. "exec-mode" must be one of:
EFFICIENT, TRACK, LIVE, VALIDATION or DYNAMIC
--stop [<vs-name> | all]
Used to stop the named virtual service (or all) in the current environment.
--performace [on|off]
Used to set performance for the current VSE
--version
Print version and exit.
--help
Displays this text.