modify Apache 2.0 license to allow warranty and service terms

[Qianqian Fang]

Dear list:

I have a question regarding modification of Apache 2.0 license to
offer warranty and additional services.

Based on Section 9 of the license 
(http://www.apache.org/licenses/LICENSE-2.0.html),
additional service terms is permitted. However, in Section 7, the work is
provided "AS IS" without warranty.

In what form I should modify Apache 2 license to allow me to

1) offer warranty to the user
2) offer itemized services, including technical support, to the user

while keeping the work legitimate under the upstream Apache 2
license?

Is it ok to delete Section 7 and add the terms regarding warranty?
is it ok to add new sections after Section 9 to detail the service terms 
and fees?

your feedback is greatly appreciated!

Qianqian