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1) Almost the same. LTE is a bit faster than plain 4G2) You can change themes on Configurations > Interface > Theme or you can try any of Substratum themes instead (but you can't change the built-in theme settings unless you "uninstall" the theme(s)).
About your first question, I forgot to mention that if you want to change the "LTE" signal icon to "4G", go to Settings > Configurations > Status Bar > System Icons > Show 4G.