How to re-render the same page with additional data - node.js

Question

I have two routing functions that have to render the same page but with different data based on the URL.But once I have rendered a page, I am unable to re-render the page, it throws an error
Error: Can't set headers after they are sent.
I have two routes like this
app.post('/abc',function(req,res){
...
res.render('template',{....})
...
});
app.get('/abc/xyz/:params',function(req,res){
...
res.render('template',{...})
...
});
I have a submit button on the /abc page that directs to /abc/xyz/params but it gives me the header error.
Then, I tried to send some data with res.json which I could later handle with AJAX, but once the submit button is pressed the rendered page is lost and hence it only returns a JSON file.
I actually am trying to update a portion of a page without reloading the whole thing,but I am unable to preserve the template once the submit button is pressed.
I even tried the HTML5 History API to change URL without refresh but that even gives me the same error.
This is my whole code
app.post('/login',function(req,res){
dbo.collection("user").find({$and:[{"email":req.body.email},{'password':req.body.password}]}).count().then(function(result){
if(result==1){
dbo.collection("user").findOne({$and:[{"email":req.body.email},{'password':req.body.password}]}, function(err, r) {
req.session.email=req.body.email;
if (err) throw err;
res.render('login', {name:r.name,email: req.body.email,password: req.body.password,status: "Match Found!"});
});
}
else{
console.log('Match not found');
res.render('error_msg', { email: req.body.email,password: req.body.password,status: "Match Not found!"});
}
});
});
app.get('/login/email/:email',function(req,res){
dbo.collection("user").findOne({"email":req.params.email},function(er,r){
if(er)
throw er;
if(r){
res.render('login',{email_search:r.name});
}
else{
res.render('login',{email_search:'No User Found!'});
}
});
});