Sharepoint Designer 2010, CSS and master page

Question

Part of my job is to be able to change the css of a Sharepoint 2010 enterprise site. I've the possibility to use Sharepoint Designer. I've used it to make a copy of v4.master, set it as master page, added a few lines:

<SharePoint:CssRegistration runat="server" name="/Style Library/... myfile.css" After="corev4.css"/>
<SharePoint:CssRegistration runat="server" name="/Style Library/... myfile.css" After="corev4.css"/>

Two questions:

1) Is there any danger in making a new master page via Sharepopint Designer if you only add these lines of code?

I've seen some people writing about Sharepoint Designer being a little risky. I'm no coder myself. My only use of SP Designer is adding these lines in a master page and editing the CSS in Style Library.

2) We have lots of subsites. When I want to change the design on just one or two of these, should I continue the same path and add a uniqe css file in Style Library and link this file in a master page copy on the subsite?

Answer 1

As far as i concern, There is no risk if you create your own master page or css file. But it is risky to change the site's default master page or css file. So Don't change default master page or css file. Create your own master page or css file. If you feel problem with your created master page or css file, they revert to the default master page or css file. It will not affect your site.

Thanks.