If you do not use the UPDATE option in a transfer then DMC will simply reject all existing records and open for you a notepad log file with those rejected records which means you will only send new records.
To avoid this error log opening etc, you can simply use a record level conditional filter during the transfer :
In the mapping tab when all is linked select any column in destination right panel on which you can exercise a filter (for example a date column) double-click on it check Use Conditional Filter and then click in top on the window on "New record" and define your condition there - do not forget to check the "Use at record level" box and save.
This way when DMC hits a record where the condition is NOT met (for example date smaller than ) that record will simply be ignored .....
Check this page of online help which explains more of this feature
Now if you need to do this type of transfer regularly use the Projects and saved Profiles then use the command line feature of DMC :
Create for each access table your transfer task and when all is properly done (conditional filters etc...) save it to a profile
DMC will add it to the main TPS Project defined by default
Check this page for more help on saving profiles
When all tables are done and Profiles saved, go in the Project manager and create a New Project, name it as per your need
Then drag and drop the created profiles from main TPS to this newly created Project
You can also order them by using the Up or Down buttons if you need a defined Order of transfering data
Check this page for more help on Projects
Now you use the command line feature to "run" all the Profiles in your Project (silently or not)
In your case use a command line like x:\dmc.exe /B:1 /S:1
Where x:\ is your path to DMC executable and where /B:1 is the NUMBER of your Project created and where /S:1 is silent or /S:0 is not silent (DMC opens up and you can "see" all profiles being treated onscreen
Check this page for more help on the command line feature
You can even call this command line batch treatment from your own application ......
On _your_ machine with the normal licence you have (on clients machines you will require additional end-user licences) Try this on test tables and you will see how easy this type of data updating can become .