migrating test db -> live db

We run several web based postgresql applications and find it difficult to
make changes in a safe and reliable manner.

We have test databases that mirror the live ones. When we have finished
making the testing the updated version, we labouriously go through and copy
all the changes onto the live system. Obviously the live system has to be
taken down during this.
Is is possible to do the following:

stop postmaster
copy all files from ~postgres/base/testdb/* -> ~postgres/base/livedb/*
restart postmaster

All the tables, indexes etc have the same names in both, but we may
add/alter columns for the new version.

Thanks

Steve

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