Angular router: how to replace param?

To navigate to particular link from current url, you can do something like this,

 constructor(private route: ActivatedRoute, private router: Router){}
 ngOnInit() {
     this.route.params.subscribe(params => {
         // PARAMS CHANGED ..    

         let id = params['projectid'];    
     });
 }
 navigate(){
     this.router.navigateByUrl(this.router.url.replace(id, newProjectId));
     // replace parameter of navigateByUrl function to your required url
 }

On ngOnInit function, we have subscribed to params so we can observe and executes our statements on any change in url parameter.

Edit

Case: where ids can be same

constructor(private route: ActivatedRoute, private router: Router){}
     projectId:string;
     userId: string;
     ngOnInit() {
         this.route.params.subscribe(params => {
             this.projectId = params['projectid']; 
             this.userId = params['userId'];
         });
     }
     navigate(){
         // for /project/:projectId/users/:userId/profile
         this.router.navigate(['/project', this.projectId, "https://stackoverflow.com/users", 
         this.userId, '/profile']);
     }