I think you can use SimHub, and a plugin for LMU, that will give you the penalty information, so that means you can turn off the LMU HUD (totally) and use an OVERLAY from SimHub to show you whe messages.
I have not checked if you can show ALL messages, but you can definitely show the penalty information - like what penatly, how many laps left until you must serve it etc.
I think it can do yellow flags too - but they are probably done on the LMU in-car "DDU" for each WEC car anyway.
Some data would come from the SimHub inbuilt plugin right away, and the rest is probably best attained by using the NeoRed plugin.
Plus, an even "better" addon for sim racing is to use Simhub and feed your mobile phone, or a tablet, as another "DDU"/screen - to show all and ANY information you could possibly want extra.
For eg, I have a tablet with the complerte field leaderboard, with gaps, last and best lap times (for all cars), class and postions per class also.
These 'extra' bits of information would be avialaibe to the real drivers, evcen if some, or a lot, is via radio from the pit crew/engineer. So having it available - whether Crew Chief or a phone/tablet etc, is still realistic really.