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in the style that they prefer
Some companies have coding standards regarding style. I think that's a good policy, as long as the style imposed is not very, very strict and has been well thought.
How do you get it so that everyone doesn't just rewrite the code
Where I'm working now we have an internal Wiki with a section on coding. Code for connecting to an existing database, for instance, is already posted there.
The "If it ain't broke don't fix it" policy is a very good one, because fixing things (and remember that these "things" are often untested) has a tendency to brake them down.
Here's my $.02: start settling some standards, with the help of others, but don't try to do everything at the same time nor fixing things that work. For instance: do design a new database connection routine, but don't put it on working programs. Instead, put it on the new ones or on new versions of the existing ones.
Also, don't forget that people have feellings too... :-)