In the future just raise such non-controversial merge requests1 in chat (as opposed to meta), and a moderator will take action.
Note that synonyms are reversible while merges are irreversible (=hard to unshuffle). This is why we often hesitate to perform merges.
1 I changed OP's original wording burninate request into merge request, because that is technically the relevant term for the planet tag. More generally, a (typically non-existent) tag name is burninated to prevent its potential future creation if the Phys.SE community decides so. See e.g. this and this meta posts. In contrast to a merge request, a burninate request requires intervention from the SE team outside Phys.SE to be implemented.