How to SetEnv for an Alias

Well, this should do it:

SetEnvIf Request_URI ^/alias1 VAR=a
SetEnvIf Request_URI ^/alias2 VAR=b
SetEnvIf Request_URI ^/alias3 VAR=c
SetEnvIf Request_URI ^/alias4 VAR=d
SetEnvIf Request_URI ^/alias5 VAR=e

If you need more flexibility on matching or conditions for some reason, you could also use mod_rewrite:

RewriteEngine On
RewriteRule ^/alias1 - [E=VAR:a]
RewriteRule ^/alias2 - [E=VAR:b]
RewriteRule ^/alias3 - [E=VAR:c]
RewriteRule ^/alias4 - [E=VAR:d]
RewriteRule ^/alias5 - [E=VAR:e]

For domain like alias the answer is:

SetEnvIf Host www\.domain\.de MAGE_RUN_CODE=default
SetEnvIf Host www\.domain\.de MAGE_RUN_TYPE=website