[Oput]

первое вроде как реализовал, вернее нашёл пример на nsis. За второе ОГРОМНОЕ спасибо. Может кому пригодиться:

Код:

Section "Section 2" Sec2
SectionEnd
 
SectionGroup "s1" Sec3
Section "Section 3"
ExecWait "cmd"
SectionEnd
SectionGroupEnd

SectionGroup "s2" Sec4
Section "Section 4"
SectionEnd
SectionGroupEnd

Function .onInit

  # This is necessary otherwise Sec3 won't be selectable for the first time you click it.
  SectionGetFlags ${Sec2} $R0
  IntOp $R0 $R0 & ${SF_SELECTED}
  StrCpy $IndependentSectionState $R0

FunctionEnd

Function .onSelChange
Push $R0
Push $R1

  # Check if Sec2 was just selected then select Sec3 and Sec4.
  SectionGetFlags ${Sec2} $R0
  IntOp $R0 $R0 & ${SF_SELECTED}
  StrCmp $R0 $IndependentSectionState +3
    StrCpy $IndependentSectionState $R0
  Goto UnselectDependentSections
    StrCpy $IndependentSectionState $R0

  Goto CheckDependentSections

  # Select Sec2 if Sec3 or Sec4 was selected.
  SelectIndependentSection:

    SectionGetFlags ${Sec2} $R0
    IntOp $R1 $R0 & ${SF_SELECTED}
    StrCmp $R1 ${SF_SELECTED} +3

    IntOp $R0 $R0 | ${SF_SELECTED}
    SectionSetFlags ${Sec2} $R0

    StrCpy $IndependentSectionState ${SF_SELECTED}

  Goto End

  # Were Sec3 or Sec4 just unselected?
  CheckDependentSections:

  SectionGetFlags ${Sec3} $R0
  IntOp $R0 $R0 & ${SF_SELECTED}
  StrCmp $R0 ${SF_SELECTED} SelectIndependentSection

  SectionGetFlags ${Sec4} $R0
  IntOp $R0 $R0 & ${SF_SELECTED}
  StrCmp $R0 ${SF_SELECTED} SelectIndependentSection

  Goto End

  # Unselect Sec3 and Sec4 if Sec2 was unselected.
  UnselectDependentSections:

    SectionGetFlags ${Sec3} $R0
    IntOp $R1 $R0 & ${SF_SELECTED}
    StrCmp $R1 ${SF_SELECTED} 0 +3

    IntOp $R0 $R0 ^ ${SF_SELECTED}
    SectionSetFlags ${Sec3} $R0

    SectionGetFlags ${Sec4} $R0
    IntOp $R1 $R0 & ${SF_SELECTED}
    StrCmp $R1 ${SF_SELECTED} 0 +3

    IntOp $R0 $R0 ^ ${SF_SELECTED}
    SectionSetFlags ${Sec4} $R0

  End:

Pop $R1
Pop $R0
FunctionEnd