Shift+Alt+Right Arrow Key will demote your bullet inside a table, whilst Shift+Alt+Left Arrow Key will promote your bullet.
This is not, strictly speaking, an answer to your question, but rather a solution to your problem. You can increase the indent by clicking on the “Increase Indent” button in the “Paragraph” group on the “Home” tab of the ribbon:
If you have musophobia (fear of mice (and rats)), you can use Alt+H
(if necessary, to select the “Home” tab of the ribbon) and Alt+AI.
As far as I know there’s no way to turn this off entirely, but the best method I’ve seen is the one given by Microsoft directly.
To indent inside a table cell, click in front of the text or numbers you want to indent, and then press
When I have had to enter indents into tables I have always done this:
Enter some obscure text where you want your indents (Example: “TABTEXT”)
Find and replace that text with a TAB by entering “^t” in the replace with box.