Mercurial : How to modify a specific revision?

Question

The Scenario is as follows:

1. I cloned a Repo locally and made some changes and then committed.

hg clone test

vim abc

hg commit

1. Say the above gives me revision 1

2. I send this revision for review.

3. I make some more changes and make another commit.

vim xyz

hg commit

1. This gives us another revision say revision 2

2. Again, I send this as a new revision for review

3. I make some more changes and have some uncommitted changes.

vim 123

1. I get a request to update revision 1 with some more changes as a priority task.

Questions::

Q1 Now how do i make changes to Revision 1 ?

Q2 How do i get the differential between revision 0 and revision 1 to update the 1st review i sent ?

Answer 1

1. There are not rebase here
2. 'hg help update' for returning back to any previous changeset (hg up, edit, commit, merge)
3. Storing unfinished 123 - commit, or shelve, or mq-patch