There exists more elegant and general solution for that purpose:
tidy.name.vector <- make.names(name.vector, unique=TRUE)
make.names() makes syntactically valid names out of character vectors. A syntactically valid name consists of letters, numbers and the dot or underline characters and starts with a letter or the dot not followed by a number.
Additionally, flag unique=TRUE allows you to avoid possible dublicates in new column names.
As code to implement
d<-read_delim(urltxt,delim='\t',)
names(d)<-make.names(names(d),unique = TRUE)