You can set -Dignition.designer.websocketMaxBinaryMessageSize=4096 (default value is 2048) in your designer launcher configuration:
This raises the maximum message size the designer will accept, which should allow you to get past this issue for testing.
In some near future release (possibly as early as 8.3.1, potentially later) we're going to change the way large notification messages are delivered to the client/designer to help work around this issue as a stopgap.
In some farther future release, we're going to change the way tag values are delivered to the client/designer completely to take better advantage of the new persistent websocket that's available as of 8.3.