I propose

Using the snippets of the wonderful Commands Snippets Glossary I would propose the following solutions.

With the cursor positioned before the period:

{Snippet}delete-next-char{/Snippet},{Wrap}
{Snippet}cursor-next-char{/Snippet}{Wrap}
{Snippet}select-next-char{/Snippet}{Wrap}
{LowerCase}{Wrap}
{NoSpacing}

With the cursor positioned after the period:

{Snippet}delete-prev-char{/Snippet},{Wrap}
{Snippet}cursor-next-char{/Snippet}{Wrap}
{Snippet}select-next-char{/Snippet}{Wrap}
{LowerCase}{Wrap}
{NoSpacing}