You can easely add 2 other Ports without disruption. Just add the 2 Ports to your LAG.
Just to say, also with LAG/Trunks you haven't more speed within one connection. You will not have 4Gbs, but 4x 1Gbs. Also be aware that the 200E have "only" 1.8Gbs NGFW Throughput. Consider to plan to upgrade your environment if you have such requirements on the throughput (e.g. 600E with 2x 10Gbs).
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