The TL for which that flag was made had no indication that the "communism" was any different than OTL. So having a cross on the national flag is definitely not too plausible.
The creator cannot just change historical fact, like dyeing techniques or parameters for naval jacks etc. because they want, in that case, their designs literally wouldn't work.
Depends again on plausibility. A pelican-in-her-piety could be set as a symbol for some charity organization in some TL because the symbolism works. But crossed swords or something ridiculous like severed phalluses or something wouldn't make much sense, the author would have to be quite thorough in setting up the circumstances for the validity of such symbolism in their TL.
But, you have no right to tell me my design is wrong, and give me something I didn't want, It's my ATL, it's my creation, I wanted the flag to be the regular Swiss flag with a Red Star in the middle, Even if you don't like it, you have no right to judge about what I want, or my ATL's people want, and I can have them want whatever I want them to flipping want, or have them chose a flag design I want them to chose, it's my ATL, it's my rules that go into the ATL,
So yes, you can have your own rules for your own personal work, but you can't judge and change the rules of my TL because they don't follow IOTL, as it's not your ATL, it's mine. You have no right to shove a design down my throat I didn't want, I can have it whatever way I want. as it's my Alternate Timeline, my rules that govern the universe and everyone and how people think and chose is all my rules, as it's my Alternate Timeline.