r - changing aesthetic ggplot2 layer object inside function -

i trying change aesthetic of geom wasnt defined in original plot call.

for example shape , size

p=iris%>%ggplot(aes(x=sepal.length,y=sepal.width,colour=species))+geom_point()+theme_bw()  change_shape=function(a){   a$layers[[1]]$aes_params[['shape']]=5   a$layers[[1]]$aes_params[['size']]=10   return(a) }  pnew=change_shape(p) p 

clone layer (l) existing plot object , have not connect original plot

clonelayer=function(l){    layer.names=c('mapping','data','geom','position',             'stat','show.legend','inherit.aes',             'aes_params','geom_params','stat_params')    x=sapply(layer.names,function(y){     b=l[[y]]      if('waiver'%in%class(b)) b=null      if(y=='geom') b=eval(parse(text=class(b)[1]))      if(y%in%c('position','stat')) {         b=gsub(y, "", tolower(class(b)[1]))       }      b   })  x$params=append(x$stat_params,x$geom_params) x$params=append(x$params,x$aes_params) x$params=x$params[!duplicated(names(x$params))] x$geom_params<-x$aes_params<-x$stat_params<-null do.call(layer,x) }