Maintaing similar but not identical versions of files

[Mark]

Hi,

I have a file that I want to copy to a bunch of servers. The file is the
config file for the MySQL database (/etc/my.cnf).
I want to make sure that it is on each server and that the basic content is
always the same, but some of the lines need to differ for each server the
file is on.
Here is the content (abbreviated):

/etc/my.cnf on server "data1":
----------------------------------
## Common part start ##
[mysqld]
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
log=/var/log/mysql/mysqld.log
log-error=/var/log/mysql/mysqld.err
## Common part end ##
## Specific part start ##
master-host=data1
replicate-do-db=1to2
## Specific part end ##
------------------------------------

/etc/my.cnf on server "data2":
-----------------------------------
## Common part start ##
[mysqld]
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
log=/var/log/mysql/mysqld.log
log-error=/var/log/mysql/mysqld.err
## Common part end ##
## Specific part start ##
master-host=data2
replicate-do-db=2to1
## Specific part end ##
-------------------------------------

So what I figured I could do is the following:
Copy the part of the file that is equal for all servers over using the
"copy" action:

[mysqld]
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
log=/var/log/mysql/mysqld.log
log-error=/var/log/mysql/mysqld.err
## Specific part start ##
## Specific part end ##

Then use an "editfiles" action to remove everything between the "## Specific
part start ##" and "## Specific part end ##" and use InsertLine to add the
specific content for each server.

This will give me what I need.
However, there are 2 things I do not like about it:
1. Since the basic file, which I copy over from the policy server, is
different than the modified final file, it gets copied over in each run,
even though it does not need to be copied, unless the common part changes.

2. Since it takes some time (maybe only a few seconds if I'm lucky, but
still) from the step that copies over the base file to the step that does
the edit to get the final version of the config file, there is a short
period in which the config file is incomplete and thus unusable. If MySQL
gets restarted just during this period, I will be missing part of the
configuration, meaning I will most likely be in trouble... 

This is only one example for this general problem of files that I need on
several servers that are almost but not exactly identical on the different
machines. Is there a better way than the one I describe above?
The only other thing I could think of is having one version of the config
file per machine on the policy server, but this means redundancy and is not
really scalable - so it is exactly the opposite of the cfengine
philosophy... Except if I have a template mechanism that generates the
various versions on the central host...

Thanks,

MARK