I take it that Sri Lanka has been officially Buddhist already, so keeping this in a new constitution wouldn’t be a change.
I’ve seen situations where Christians have benefited through their neighbors’ practice of non-Christian faiths. “Secular” might be further from God than Buddhism is, depending on the situation and what is vying with Buddhism.
I pray for wisdom for the Christians in the situation to have the right witness.
I thought Buddhism isn’t really a religion at all; do they have a deity?