Some of the comments made above are not correct.
pqtaxation states:
It is that disposition that has to be changed, if possible and in accordance with the applicable laws of the country of residence of the foreign domiciliary
king-maker states:
I assume you are aware that an IOV needs the agreement of all the beneficaries
Any Deed of Variation (DoV) is not require to conform to the laws of the non-UK domiciled testator. The issue is one of UK law.
Only the beneficiaries who are affected by the DoV are required to sign it ie not all of them.
Thus, a UK domiciled beneficiary could execute a DoV in favour of the children pursuant to which no UK IHT would arise even if the UK domiciliary died within 7 years of execution of the DoV; this would of course require that the conditions of s 142 IHTA 1984 (eg execution within 2 years) are satisfied.