Customizing the sharepoint document set - sharepoint

Question

I have to customize sharepoint 2013 document set welcome page(document set properties web part) and
I am not able to find the document set home aspx page
Can I use any client context model to fetch the data and display doc set properties.

Answer 1

Just create a new content type inheriting from Document Set, add the extra columns and set which ones need to be shown on the welcome page via the Document Set settings link when editing the Content Type. Also under the Document Set settings page you can click on 'Customize the Welcome Page' which allows you to edit the page just like any other web part page.
On the second point the client context will need to be connected to the web that contains the list and specific document set you're after, the identity used to connect will need permissions to the document set.
Edit:
To customize the look and feel by injecting JavaScript/CSS you'll need to make use of the ScriptLink custom action.
This lets you inject a custom piece of JavaScript into all pages. In the script you'll need logic to determine if the custom CSS should be applied, and if so Inject it.
The C# for injecting a script block via ScriptLink Custom Action:
public void AddJsLink(ClientContext ctx, Web web)
{
string scenarioUrl = String.Format("{0}://{1}:{2}/Scripts", this.Request.Url.Scheme,
this.Request.Url.DnsSafeHost, this.Request.Url.Port);
string revision = Guid.NewGuid().ToString().Replace("-", "");
string jsLink = string.Format("{0}/{1}?rev={2}", scenarioUrl, "injectStyles.js", revision);
StringBuilder scripts = new StringBuilder(#"
var headID = document.getElementsByTagName('head')[0];
var");
scripts.AppendFormat(#"
newScript = document.createElement('script');
newScript.type = 'text/javascript';
newScript.src = '{0}';
headID.appendChild(newScript);", jsLink);
string scriptBlock = scripts.ToString();
var existingActions = web.UserCustomActions;
ctx.Load(existingActions);
ctx.ExecuteQuery();
var actions = existingActions.ToArray();
foreach (var action in actions)
{
if (action.Description == "injectnavigation" &&
action.Location == "ScriptLink")
{
action.DeleteObject();
ctx.ExecuteQuery();
}
}
var newAction = existingActions.Add();
newAction.Description = "injectnavigation";
newAction.Location = "ScriptLink";
newAction.ScriptBlock = scriptBlock;
newAction.Update();
ctx.Load(web, s => s.UserCustomActions);
ctx.ExecuteQuery();
}
Then your JavaScript would have something like:
if(window.location.href.indexOf(patternToMatchToDocSetpage)>-1) {
var link = document.createElement("link");
link.href = "http://example.com/mystyle.css";
link.type = "text/css";
link.rel = "stylesheet";
document.getElementsByTagName("head")[0].appendChild(link);
}
I'd advise you to take a look at the relevant PnP sample on script link injection