It should be something along the lines of
tau_parameters = 0.1:0.3:0.8;
temp_mat=NaN(size(oo_.steady_state,1),length(tau_parameters));
for i=1:length(tau_parameters)
set_param_value('varpi',tau_parameters(i));
[oo_.steady_state,M_.params,info] = steady_(M_,options_,oo_);
if ~info
temp_mat(:,i)=oo_.steady_state;
end
end;
plot(tau_parameters,temp_mat(strmatch('Y',M_.endo_names,'exact'),:))