It's possible to override the default values for the cluster initialization by setting environment variables. The defaults can be found in the file 'default_args.bash'. Here an example to override name of the first node of the cluster:
export MASTER_NAME=192.168.7.141
./init_cluster.bash
Setting variable ADMIN_NAME to couchbase
Setting variable ADMIN_PWD to couchbase
Variable MASTER_NAME is already set
Setting variable NODE_NAME to ubuntu-cb-node
Setting variable RAM_SIZE to 1024
Setting variable DATA_DIR to /opt/couchbase/var/lib/data
Setting variable IDX_DIR to /opt/couchbase/var/lib/idx
Initializing the node ...
SUCCESS: set hostname for 192.168.7.141
Initializing the cluster ...
SUCCESS: init/edit 192.168.7.141
export MASTER_NAME=192.168.7.141
export NODE_NAME=192.168.7.142
./add_node.bash
Setting variable ADMIN_NAME to couchbase
Setting variable ADMIN_PWD to couchbase
Variable MASTER_NAME is already set
Variable NODE_NAME is already set
Setting variable RAM_SIZE to 1024
Setting variable DATA_DIR to /opt/couchbase/var/lib/data
Setting variable IDX_DIR to /opt/couchbase/var/lib/idx
Initializing the node ...
SUCCESS: set hostname for 192.168.7.142
Adding the node to the cluster ...
SUCCESS: server-add 192.168.7.142:8091
INFO: rebalancing .
SUCCESS: rebalanced cluster
export MASTER_NAME=localhost
export BUCKET_NAME=bash_examples
export BUCKET_PWD=hello
./create_bucket.bash
Setting variable ADMIN_NAME to couchbase
Setting variable ADMIN_PWD to couchbase
Variable MASTER_NAME is already set
Variable NODE_NAME is already set
Setting variable RAM_SIZE to 1024
Setting variable DATA_DIR to /opt/couchbase/var/lib/data
Setting variable IDX_DIR to /opt/couchbase/var/lib/idx
Setting variable BUCKET_SIZE to 128
Variable BUCKET_NAME is already set
Variable BUCKET_PWD is already set
Setting variable BUCKET_REPL to 1
Creating the bucket ...
...SUCCESS: bucket-create