connection string - Using different environment in development and production with SSIS -

my ssis (2005) package uses variables , expressions set values @ run-time (e.g. connection string, database name)

i have found out package validation not use expressions need supply "default" value (which never used @ run-time)

my problem how set default value work on both development machine , in production.

an example:
have connection manager connectionstring property set expression @[user::currentconnectionstring].

at run-time currentconnectionstring fetched database.

the package validator use default value connectionstring property need put there or validation fail.

my problem need different connection strings on development machine , on production server (e.g. different user name).

currently manually edit dtsx file before deploying production. is there better way?