When a UTF8 or UTF16 transfer is done using XCOM you specify CODE=UTF8 on z/OS or CODE_FLAG=UTF8 (in Windows and Unix) and specify in parameters LOCAL_CHARSET and REMOTE_CHARSET the Coded Character Set Identifier (CCSID) for the sending and receiving side. Can the tables contained be changed at will?
The Coded Character Set Identifier (CCSID) itself is not a Code table like EBCDIC or ASCII or ISO-8559 but a collection of one or more Code Tables. You cannot change the content of a code table as everyone relies on. If necessary choose a different CCSID for the transfer. A list of valid CCSID-Numbers and their name is available here: https://www-01.ibm.com/software/globalization/ccsid/ccsid_registered.html
A coded character set identifier (CCSID) contains all of the information necessary to assign and preserve the meaning and rendering of characters through various stages of processing and interchange. This information always includes at least one code page, but may include multiple code pages of differing byte-lengths. The CCSID also has an associated encoding scheme that governs how various code points are to be handled. This mechanism allows a program to recognize bidirectional orientation, character shaping (mainly of Arabic characters), and other complex encoding information.