Caniateir diwygiadau i Ddeddfau Trethi Cymru hefyd er mwyn ymateb i amgylchiadau allanol eraill, megis i sicrhau nad yw trethi datganoledig Cymru yn cael eu gosod lle byddai gwneud hynny yn anghydnaws ag unrhyw rwymedigaethau rhyngwladol.
Amendments to the Welsh Tax Acts will also be permitted in order to respond to other external circumstances, such as to ensure the devolved Welsh taxes are not imposed where to do so would be incompatible with any international obligations.