Syntax:
ALTER RESOURCE GROUP group_name
    [VCPU [=] vcpu_spec [, vcpu_spec] ...]
    [THREAD_PRIORITY [=] N]
    [ENABLE|DISABLE [FORCE]]

vcpu_spec: {N | M - N}

ALTER RESOURCE GROUP is used for resource group management (see
https://dev.mysql.com/doc/refman/8.0/en/resource-groups.html). This
statement alters modifiable attributes of an existing resource group.
It requires the RESOURCE_GROUP_ADMIN privilege.

group_name identifies which resource group to alter. If the group does
not exist, an error occurs.

The attributes for CPU affinity, priority, and whether the group is
enabled can be modified with ALTER RESOURCE GROUP. These attributes are
specified the same way as described for CREATE RESOURCE GROUP (see
[HELP CREATE RESOURCE GROUP]). Only the attributes specified are
altered. Unspecified attributes retain their current values.

The FORCE modifier is used with DISABLE. It determines statement
behavior if the resource group has any threads assigned to it:

o If FORCE is not given, existing threads in the group continue to run
  until they terminate, but new threads cannot be assigned to the
  group.

o If FORCE is given, existing threads in the group are moved to their
  respective default group (system threads to SYS_default, user threads
  to USR_default).

The name and type attributes are set at group creation time and cannot
be modified thereafter with ALTER RESOURCE GROUP.

Examples:

o Alter a group CPU affinity:

ALTER RESOURCE GROUP rg1 VCPU = 0-63;

o Alter a group thread priority:

ALTER RESOURCE GROUP rg2 THREAD_PRIORITY = 5;

o Disable a group, moving any threads assigned to it to the default
  groups:

ALTER RESOURCE GROUP rg3 DISABLE FORCE;

Resource group management is local to the server on which it occurs.
ALTER RESOURCE GROUP statements are not written to the binary log and
are not replicated.

URL: https://dev.mysql.com/doc/refman/8.0/en/alter-resource-group.html

