Solution for @aloiscochard

gistfile1.scala

// Internal function
def update[L1 <: HList, L2 <: HList](k: Key, fs: L1)(ts: L2 => L2)(implicit e: CoNatTRelAux[L1, Field, L2, Id])

// Function used by client                                                                                                       
def update[P1 <: Product, P2 <: Product, L1 <: HList, L2 <: HList, F](k: Key)(fs: P1)                                             
  (implicit
    h1: HListerAux[P1, L1],
    e: CoNatTRelAux[L1, Field, L2, Id],
    h2: HListerAux[P2, L2],
    t: TuplerAux[L2, P2],
    unhl : FnUnHListerAux[L2 => P2, F],
    hl : FnHListerAux[F, L2 => P2]) =
  new Update[L1, L2, P2, F](k, fs.hlisted)                                                                                            
                                                                                                                                                     
class Update[L1 <: HList, L2 <: HList, P2 <: Product, F](k: Key, fs: L1)
  (implicit
    hl : FnHListerAux[F, L2 => P2], 
    h2: HListerAux[P2, L2],
    e : CoNatTRelAux[L1, Field, L2, Id]) {
  def to(ts: F) = {
    val hts = (l2 : L2) => (ts.hlisted(l2).hlisted)
    update(k, fs)(hts)(e)
  }
}                                                                                                                              
 
// USED THAT WAY
update(c.key)(key, name).to((a, b) => (a, b + "*"))