LyX enumeration style from numbers to letters

Short answer

• To get a), add this to the preamble: \renewcommand{\labelenumi}{\alph{enumi})}
• To get [a], add this to the preamble: \renewcommand{\labelenumi}{[\alph{enumi}]}

If you don't want the change to occur globally, then add this code right before the enumeration (and resotre right after, if needed).

Long answer

In the preamble, use the \renewcommand{indicator}{format} syntax for each level of heirarchy you would like to change (4 level max. are supported), where indicator is either of the following label indicators:

1. \labelenumi -- 1st level
2. \labelenumii -- 2nd level
3. \labelenumiii -- 3rd level
4. \labelenumiv -- 4th level

and format is a macro consisting of enumerators and styles.

The style can be any of the following:

• \arabic{enumerator}, for 1, 2, 3, ...
• \alph{enumerator}, for a, b, c, ...
• \Alph{enumerator}, for A, B, C, ...
• \roman{enumerator}, for i, ii, iii, ...
• \Roman{enumerator}, for I, II, III, ...

The enumerator can be any of the following:

1. enumi -- 1st level
2. enumii -- 2nd level
3. enumiii -- 3rd level
4. enumiv -- 4th level

I personally prefer the 1.4.2 a) repeating format, for which you need:

\renewcommand{\labelenumi}{\arabic{enumi}.}
\renewcommand{\labelenumii}{\labelenumi\arabic{enumii}.}
\renewcommand{\labelenumiii}{\labelenumii\arabic{enumiii}}
\renewcommand{\labelenumiv}{\alph{enumiv})}

Write into Document->Settings->Preamble:

\usepackage{enumitem}
\setenumerate{label=A)}
\setenumerate[2]{label=a)}

For deeper values use also [3], [4]. Inside LyX you will still see the 1. If you want to change this too, then you'll have to rewrite your LyX layout file.

You can set custom labels for individual items:

1. Use the default "Numbered list" environment in LyX (select from the menu or use the keyboard shortcut ^P E).

2. Insert a "Custom Item" inset: Open the context menu via Ctrl+click/right click over a list element and select "Custom Item".

3. In the Custom Item inset, enter a custom label for this particular item.

You will see the default labels in LyX, but the output will use the label from the "Custom Item" box. In LyX:

1. Custom Item[A] Fruits:

a) Custom Item[A.1] orange

b) Custom Item[A.2] apple

will produce in the output file:

A Fruits:

A.1 orange

A.2 apple