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added 12 characters in body
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Kuba
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Define your rule as a function:

ruleDerF = ( # /. Module[{x},  Derivative[n_][f][var_] :> (D[x f[x], {x, n - 1}] /. x -> var) ]) &;& f''[x] // ruleDerF 
f[x] + x Derivative[1][f][x] 
 FixedPoint[ruleDerF, f''[x]] 
f[x] + x^2 f[x] 
FixedPoint[ruleDerF, f''[1]] 
2 f[1] 

(havent tested heavily)

Define your rule as a function:

ruleDerF = ( # /. Derivative[n_][f][var_] :> (D[x f[x], {x, n - 1}] /. x -> var) ) &; f''[x] // ruleDerF 
f[x] + x Derivative[1][f][x] 
 FixedPoint[ruleDerF, f''[x]] 
f[x] + x^2 f[x] 
FixedPoint[ruleDerF, f''[1]] 
2 f[1] 

(havent tested heavily)

Define your rule as a function:

ruleDerF = (# /. Module[{x},  Derivative[n_][f][var_] :> (D[x f[x], {x, n - 1}] /. x -> var) ])& f''[x] // ruleDerF 
f[x] + x Derivative[1][f][x] 
 FixedPoint[ruleDerF, f''[x]] 
f[x] + x^2 f[x] 
FixedPoint[ruleDerF, f''[1]] 
2 f[1] 

(havent tested heavily)

Source Link
Kuba
  • 138.9k
  • 13
  • 297
  • 803

Define your rule as a function:

ruleDerF = ( # /. Derivative[n_][f][var_] :> (D[x f[x], {x, n - 1}] /. x -> var) ) &; f''[x] // ruleDerF 
f[x] + x Derivative[1][f][x] 
 FixedPoint[ruleDerF, f''[x]] 
f[x] + x^2 f[x] 
FixedPoint[ruleDerF, f''[1]] 
2 f[1] 

(havent tested heavily)