migrating from one SQL cluster to another cluster I have 2 existing SQL clusters. Both 2008 R2. Each have unique instance names.

Server1\inst1

ServerA\reports.

We are decommissioning Server1 cluster and need to migrate DBs over to ServerA\reports

So I don't have to change application and SSRS report connection strings is it possible to add a SQL alias of Server1\inst1 to ServerA\reports.

If possible this would allow you to connect using either Server1\inst1 or ServerA\reports.

Thanks,

-Jess-
Rename New Server

Is ServerA\reports running existing software that will break if the name changes? If not, after decommissioning Server1\inst1 you could rename the entire failover cluster instance and network name to reflect the decommissioned instance. 

Alias

You can create an alias in SQL Server Configuration Manager on the server that is running SSRS with the alias name Server1\inst1 pointing to ServerA\reports. SSRS should be able to use this to connect with reports.

Shared Data Source

Alternatively, if you alter your reports to use a single shared data source per database you can have a single data source for each in SSRS that you can update. I do this to alter between a primary and backup set of reporting data as a form of local redundancy.

Edit: Reference for creating an alias: https://msdn.microsoft.com/en-us/library/ms190445.aspx

Note that you'll need to create the alias on the 'client' server rather than the server hosting SQL, so in your case on the server running SSRS where the connection is initiated from.