Are db_recovery_file_dest and db_recovery_file_dest_size parameter dynamic or static?
The isinstance_modifiable flag only tells you whether that parameter can be set differently for different instances (for RAC) or not. For the parameters you're looking at, it is false, meaning that all instances in a single RAC cluster must have the same values.

If you want to know when you can change a parameter, look at two other columns in that table:


isses_modifiable: if TRUE, the parameter can be changed with alter session
issys_modifiable: tells you about changes that can be made with alter system.


IMMEDIATE means yes and changes take effect immediately,
DEFERRED can be changed, but will only take effect at next start,
FALSE can only be changed if you used an spfile to start the instance, and changes only take effect on next start.



Complete details are available in the v$parameter documentation.