Argthtjtr

I am trying to cite my reference with the following structure

author a/author b/author c, year

with slashes and without spaces between the authors in the author year style. You can find a MWE below. As a precaution, I have included all commands related to my bibliography in case there might be somecomplications with the already existing changes.

documentclass[article, bibtotocnumbered,liststotoc,12pt]{scrartcl}

usepackage[T1]{fontenc}

usepackage[latin1]{inputenc}

usepackage[ngerman]{babel}

usepackage[paper=a4paper,left=50mm,right=20mm,top=20mm,bottom=20mm]{geometry} %define margins..

geometry{a4paper} 

usepackage{lmodern}





usepackage{filecontents}



%Bibliotheken

usepackage

[style=ext-authoryear,labelnumber, useprefix=true,

sorting=nyt,maxbibnames=9,maxcitenames=3,uniquelist=false, backend=biber, 

doi=false,isbn=false,url=false,

uniquename=false,bibencoding=utf8, date=year, giveninits=true, terseinits=false, dashed=false]

{biblatex}





%Remove Dot after volume

renewbibmacro*{volume+number+eid}{%

  printfield{volume}%

%  setunit*{adddot}% DELETED

 % setunit*{addnbspace}% NEW (optional); there's also addnbthinspace

  printfield{number}%

  setunit{addcommaspace}%

  printfield{eid}}

DeclareFieldFormat[article]{number}{mkbibparens{#1}}



% Number of articles in parentheses

DeclareFieldFormat[article]{number}{mkbibparens{#1}}



%Dot after journal title

DeclareFieldFormat{journaltitle}{{#1}isdot}



renewbibmacro*{journal+issuetitle}{%

  usebibmacro{journal}%

  setunit*{addcommaspace}%

  iffieldundef{series}

    {}

    {newunit

     printfield{series}%

     setunit{addspace}}%

  usebibmacro{volume+number+eid}%

  setunit{addspace}%

  usebibmacro{issue+date}%

  setunit{addcolonspace}%

  usebibmacro{issue}%

  newunit}





%Dort und Sorting Last-First

DeclareNameAlias{sortname}{first-last-bold}



DeclareNameFormat{first-last-bold}{mkbibbold{%

  ifgiveninits

    {usebibmacro{name:last-first}{namepartfamily}{namepartgiveni}{namepartprefix}{namepartsuffix}}

    {usebibmacro{name:last-first}{namepartfamily}{namepartgiven}{namepartprefix}{namepartsuffix}}%

  usebibmacro{name:andothers}}}





begin{filecontents}{jobname2.bib}

@Article{Hansen2011,

  author  = {Hansen, Peter R. and Lunde, Asger and Nason, James M.},

  title   = {The Model Confidence Set},

  journal = {Econometrica},

  year    = {2011},

  volume  = {79},

  number  = {2},

  pages   = {453-497},

  url     = {https://EconPapers.repec.org/RePEc:ecm:emetrp:v:79:y:2011:i:2:p:453-497},

}



end{filecontents}

addbibresource{jobname2.bib} 



begin{document}

textcite{Hansen2011}

printbibliography

end{document}

With

DeclareDelimFormat{multinamedelim}{addslash}

DeclareDelimAlias{finalnamedelim}{multinamedelim}

you turn the delimiters to slashes in all contexts. With

DeclareDelimFormat[bib,biblist]{multinamedelim}{addcommaspace}

DeclareDelimFormat[bib,biblist]{finalnamedelim}{%

  ifnumgreater{value{liststop}}{2}{finalandcomma}{}%

  addspacebibstring{and}space}

you get back commas and "and" in the bibliography.

Here is a modernised version of your MWE that makes use of biblatex-ext features (volnumdelim and jourvoldelim) as well as features new to biblatex 3.12 (DeclareNameWrapperFormat) to achieve the same output more elegantly.

documentclass[12pt, bibliography=totocnumbered, listof=totoc]{scrartcl}

usepackage[T1]{fontenc}

usepackage[utf8]{inputenc}% UTF-8 is the usual encoding in modern editors,

                           % it's even the default for modern LaTeX versions

usepackage{lmodern}

usepackage[ngerman]{babel}

usepackage{csquotes}





usepackage[backend=biber, style=ext-authoryear,

  maxbibnames=9, maxcitenames=3, uniquelist=false, uniquename=false,

  useprefix=true, giveninits=true, dashed=false

  doi=false,isbn=false,url=false,

  date=year]{biblatex}



DeclareNameAlias{sortname}{family-given}

DeclareNameWrapperFormat{sortname}{mkbibbold{#1}}



DeclareDelimFormat{multinamedelim}{addslash}

DeclareDelimAlias{finalnamedelim}{multinamedelim}



DeclareDelimFormat[bib,biblist]{multinamedelim}{addcommaspace}

DeclareDelimFormat[bib,biblist]{finalnamedelim}{%

  ifnumgreater{value{liststop}}{2}{finalandcomma}{}%

  addspacebibstring{and}space}



DeclareFieldFormat{journaltitle}{#1isdot}

renewcommand*{volnumdelim}{}

DeclareFieldFormat[article]{number}{mkbibparens{#1}}



renewcommand*{jourvoldelim}{addcommaspace}



usepackage{filecontents}

begin{filecontents}{jobname.bib}

@Article{Hansen2011,

  author  = {Hansen, Peter R. and Lunde, Asger and Nason, James M.},

  title   = {The Model Confidence Set},

  journal = {Econometrica},

  year    = {2011},

  volume  = {79},

  number  = {2},

  pages   = {453-497},

  url     = {https://EconPapers.repec.org/RePEc:ecm:emetrp:v:79:y:2011:i:2:p:453-497},

}



end{filecontents}

addbibresource{jobname.bib} 



begin{document}

textcite{Hansen2011}

printbibliography

end{document}