This policy setting allows you to check or uncheck the "Type and Replace" checkbox found under File tab | Options | Advanced. ...

This policy setting allows you to check or uncheck the "Type and Replace" checkbox found under File tab | Options | Advanced.  This checkbox may only be shown when certain South East Asian languages, such as Thai or Vietnamese, are enabled.South Asian languages follow stringent grammatical rules that dictate which textual character elements are allowed next to one another in the composition of words. To compound the complexity of correctly entering South Asian characters, text includes both simple characters and characters that include one or more markings such as diacritics, tone marks, vowels, and accents— for example, in Thai, leading vowels are normally followed by a consonant that does or does not include vowel markings, but diacritics are located below it.To assist you in correctly entering characters in your document that prescribe to the grammar rules for the enabled South Asian language, Word can automatically check the text for you. Word can also make logical substitutions for you by using Type and Replace, a complementary feature.Sequence checking can be used by itself or in combination with Type and Replace. When sequence checking only is selected, Word will not allow an invalid character to be typed at the insertion point. If Type and Replace is also selected, Word will insert or replace an existing character to make a valid sequence.If you enable or do not configure this policy setting, the "Type and Replace" checkbox is checked.If you disable this policy setting, the "Type and Replace" checkbox is unchecked.