In old versions of DBT, if you had a template set up to default to Grade 1 or Grade 2 braille, it was possible for authors to change the grade using the Layout: Translation Codes menu, or equivalent keystrokes.
From DBT 10.6 on, four new codes were introduced which can only be used by either inserting the codes into the "initial" style in a template or by manually inserting the codes into the document. This is intentional, and designed to prevent undesired changes.
The two codes are [g1l] and [g2l]. The last character is L as in Lima or lock. These work the same way as the [g1] and [g2] codes, but they cannot be overridden in the usual way.
If it is essential to switch grades mid-document, you must manually insert the [g1u] (u as in unlock) or [g2u] at the appropriate place in the text.