Replace a base64 value from file

I have one file which is gets details from ldapsearch command and create file as below # lschuler, people, pl.s2-eu.XXXXXXXXX.local dn: uid=lschuler,ou=people,dc=pl,dc=s2-eu,dc=XXXXXXXXX,dc=local objectClass: posixAccount objectClass: inetOrgPerson objectClass: organizationalPerson objectClass: person loginShell: /bin/bash homeDirectory: /home/lschuler gidNumber: 10000 uid: lschuler cn: Leonie Schuessler uidNumber: 20056 mail: XXXXXXXX@XXXXXXXXX.com sn: Schuessler givenName: Leonie # cadelie, people, pl.s2-eu.XXXXXXXXX.local dn: uid=cadelie,ou=people,dc=pl,dc=s2-eu,dc=XXXXXXXXX,dc=local objectClass: posixAccount objectClass: inetOrgPerson objectClass: organizationalPerson objectClass: person loginShell: /bin/bash homeDirectory: /home/cadelie gidNumber: 10000 uid: cadelie cn:: Q2hsb8OpIEFkw6lsaWU= uidNumber: 20057 mail: XXXXXXX@XXXXXXXXX.com sn:: QWTDqWxpZQ== givenName:: Q2hsb8Op if you see **sn::** & **givenName::** some times have base64 value I want to decode it with command which I am not able to do cat file.text | sed -e "s/.*sn:: //g;s/;.*//" |base64 -d && cat file.text | sed -e "s/.*givenName:: //g;s/;.*//" |base64 -d how I can decode only sn:: & givenName:: which has base64 value and save to same file again. Please help, SAMURAI