Recently I came across a question on SDN asking how the Low Cost Country flag is set during data load, so I decided to clarify this with a short post.
When you load data for InfoObject 0XACOUNTRY you can specify whether this flag is set in attribute 0XSARLCCFLG. When you load data to Source System Supplier (0XALOCSUPP) using Data Management, the country attribute (0XSARCNLSP) is used to lookup the country master data to see whether this flag is set. If so, it will be copied into the 0XALOCSUPP master data.
This means that at load time it is decided which suppliers have this flag set. If the country field of the supplier were to change, this would trigger a delta that would also update the Low Cost Country Flag for that supplier.
Generally it is fixed whether or not a particular country has this flag set or not. In the case that this changes, however, it would be necessary to do a full load of 0XALOCSUPP, or to take some other measure (e.g. manually updating the relevant master data).