You can create "adjacent"/linked demiplanes with different planar traits, however. Such as entering a cave or a house in one demiplane that is actually a different demiplane when "inside."
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I believe you can though its ambiguous enough to require GM ruling. The relevant section that makes me believe this is this part in create lesser demi-plane.
If you are within the demiplane, you can add to its area by casting the spell again. Alternatively, you may cast this spell again to reset the duration of an existing area to that of your latest casting. If the duration on one area of the demiplane ends and other parts remain, creatures in the expiring area are shunted to remaining areas.
Everything else say's "as per lesser". As you can see above you "add to the spells area" by recasting the spell but if the duration of one area ends it disolves only that area. So as per the spell I believe your demiplane is meant to be like the old family quilts people used to do. That is to say even if the demiplane is visually one area it structurally is a bunch of different ones. That you can walk between and not tell any difference from? So if you cast the spell 9 times you wouldn't have one plane but nine connected ones. In which case since each plane is seperate you could give them their own unique traits. So you stand in the central sunny beach themed plane and if you look north you see the snowy forest part of the plane and if you look west you see the cave part of the plane and so on.
Personally I dislike this and houserule it otherwise (its one plane, all same traits, all dissolves at once) but per the description in the spell it feels like you can give each part of the plane its own traits as long as it was created by a second, third casting. However the wording is bad as it also say's you increase the area and then refers to the existing area.