Siemens SIMATIC PCS 7 Operation And Maintenance page 85

Range of DB and FC numbers
The range of DB and FC numbers can be neither compressed nor modified; otherwise, a
complete download with the CPU in STOP will be required.
Changing block types
If you need to change a block type already in use, remember that interface changes will
require a complete download of the AS. Such changes are:
● Adding inputs/outputs
● Making a block capable of signaling
● Changing initial values
As an alternative, you should create reserve variables from the start when you generate a
block.
You can find more information in FAQ: What should you watch out for when defining the
program blocks to ensure that the CPU does not go into "STOP" status during downloading
whenever its interfaces have to be changed again in the future?
(https://support.industry.siemens.com/cs/ww/en/view/13298050)
Compendium Part D - Operation and Maintenance (V9.0)
Operating Manual, 02/2018, A5E43228948-AA
AS and OS expansions
7.2 Program changes
85