RMAN - ready only TS backup and recovery

Database: RAC - 4 nodes

ASM

OS: Linux 6

DB size: 55 TB

Read only TS: 1 TB

I need to Backup six read only tablespaces and have the following questions:

My understanding is that after I run the following commands for each tablespaces, and  I understand my first backup database run will include the data file of the Read Only Tablespace.

  alter tablespace tbs1 read only;

alter tablespace tbs2 read only;

alter tablespace tbs3 read only;

I have retention period of 30 days.  let say, I need to restore these six tablespaces after one year without affecting the existing database, how would I take care of this?  Presently backing up on tape via net backup. Do I need to add any more steps in my backup script to exclude these tablespaces?