Manipulate changing controls

There are various viewers available that could used to switch between different arrangements of controls. For a seamless look, one might use PaneSelector. If type is to have its own control, putting it inside each of the panes ensures Manipulate will align them.

Manipulate[
 {x, yyy},
 {{x, a}, {a, b, c, d}, None},
 {{yyy, 0.5}, 0, 1, None},
 {{type, 1}, Range@3, None},
 PaneSelector[{
   1 -> Column[{
      Control@{x, {a, b, c, d}, RadioButtonBar},
      Control@{{yyy, 0.5}, 0, 1},
      Control@{type, Range@3}
      }],
   2 -> Column[{
      Control@{x, {a, b, c, d}, SetterBar},
      Control@{yyy},
      Control@{type, Range@3}
      }],
   3 -> Column[{
      Control@{x, {a, b, c, d}, PopupMenu},
      Control@{{yyy, 0.5}, 0, 1},
      Control@{type, Range@3}
      }]
   }, Dynamic@type]     
]

---

Comment: Your question suggests you might be seeking rather fine control over the UI. It might be easier in the long run to build it from the ground up with DynamicModule and the various user interface features Mathematica offers.

Manipulate[

 Which[
  typeSelected == 1,Row[{"you selected type 1 UI with input h = ", h}],
  typeSelected == 2,Row[{"you selected type 2 UI with input mass = ", m}],
  True, "No way ! Please report a bug"]
 ,

 Grid[{
   {Style["A self modifying dynamic Manipulate UI" , 10], SpanFromLeft},

   {"Which UI would you like to see?", 
    TabView[{
      {1,"type 1" ->Row[{"h? ", SetterBar[Dynamic[h, {h = #} &], {0, 1, 2}]}]},
      {2,"type 2" -> Row[{"mass= ",Manipulator[Dynamic[m, {m = #} &], {0, 100, 1}], 
          Dynamic[m]}]}
      }, Dynamic[typeSelected]
     ]
    }
   }, Frame -> All, Spacings -> .5, FrameStyle -> Gray],

 {{h, 1}, None},
 {{m, 4}, None},
 {{typeSelected, 1}, None},
 TrackedSymbols :> {h, m, typeSelected}     
 ]

Using the command

 ControlType ->

and then listing the type of control you want, such as SetterBar, Manipulator, or Slider at the end of your Manipulate function allows you to customize the controls. Mathematica will also automatically change the control based on the data put in (i.e., if you put in code like this {frame, {True, False}} it will give a checkbox).