Advice on changing retention period

We are looking at changing the retention period for our replication
from 14 days to 21 days and before doing so wanted to get some advice.

1) Most importantly, if I make the change, will it force the
subscribers to reinitialise or cause any other similar operational
issues or will it be fairly transparent as far as the clients are
concerned?
2) Is it best to use sp_changemergepublication?
3) Are there major disadvantages to increasing the retention period as
suggested (I know it will increase the amount of metadata but is this
a major issue)?

The server is running SQL Server 2005 and set up as publisher and
distributor. There are (or will be) approximately 150 clients all
running SQL Server 2005 Express. All merge pull subscriptions and web
synchronisation.

Any advice greatly appreciated.

Jeremy.

Hi Hilary,
for merge I don't see a requirement to reinitialize after an increase of
retention period - perhaps you are referring to problems encountered when the
retention period is reduced and subscribers exceed the retention period, or
maybe a republishing issue?
Many thanks,
Paul Ibison