I am not sure on which environment you are. If you are on UNIX you can use following.

export this at very start of your unix script

export TAG_0 =LEVEL0_`date`

you can see man date and can use option like `date +%d or +%m`

and in run block give follwing

RMAN> run {
2> backup as compressed backupset database tag '$TAG_0';
3> backup archivelog all delete all input tag ''$TAG_0';
4> }