Question: One of my SSL certificates (simple domain verification only) is about to expire on windows 2003 IIS 7.0 server.

I got better offer from another vendor, and the guys who originally issued my certificate do not want to negotiate lower prices.

Anyway - going trough the certificate wizard in IIS, I have the option to "renew" or to "uninstall" and then install a new certificate.

So - can I use the "renew" option to create a certificate request and pass this to the new vendor, or I need to start with "new" request? Will it matter for the new vendor, that the previous certificate was issued by another signer?

The problem is, that I do not want to stop the server (the secured part at least) because of removing the old certificate and creating new CSR, and wait for the new certificate to install.

Or, is there an option to prepare a new CSR without removing the old certificate?

Answer: 
You only need to create a temporary website with IIS 6.0. IIS 7.0 allows you to create multiple pending requests at a time.

IIS 7.0 actually has a bug that causes the renew function to generate a CSR with a very large key (much larger than you want). Because of this, it is recommended that you create a new pending request instead of selecting the renew option. Once installed you simply switch the SSL binding on the website and you won't have any downtime. This also allows you to generate a new key every time you renew which increases security.

The certificate provider (CA) doesn't care whether you use the new option or the renew option and you could use either option whether you are staying with the same CA or ordering from a new one.
OK, to partially answer my own question - the part of creating/using a new certificate without removing the existing one (i.e. without stopping the server), I found a good description [on Comodo website](https://support.comodo.com/index.php?_m=knowledgebase&_a=viewarticle&kbarticleid=456) - basically I need to create a "temporary" website on the server, and use it to create a new CSR, send it for signing, and receive and import the certificate.

Then on my main (real) site I need to replace the current certificate, and then delete the temp one.