Still it is not renaming Tmid-T0 and Limit columns. 
Look code
using HTTP , CSV, DataFrames
function doanalysis()
dfg=nothing
for x in 34000:34146
print("\r peeking at GCN $x ")
try
url = "https://gcn.nasa.gov/circulars/$x/raw"
resp = HTTP.get(url)
status=resp.status
print(" ",status," ");
if status == 404 ; println("status=",status); continue; end
txt = String(resp.body)
grb_rexp=r"GRB ?\d{6}([A-G]|(\.\d{2}))?"
m=match(grb_rexp,txt)
grb="nogrb"
if occursin(grb_rexp,txt)
print(m.match)
grb=m.match
end
function dframe()
df.GCN=[x for i in 1:nrow(df)]
df.GRB=[grb for i in 1:nrow(df)]
if isnothing(dfg)
dfg=df
else
dfg=vcat(dfg,df,cols=:union)
end # if x is first
end # dframe
if occursin("V. Lipunov", txt)
println(" MASTER report")
he=first(findfirst(r"^Tmid"im,txt))
lr=first(findnext("\nFilter",txt,he))-1
cltxt=txt[he:lr]
df=CSV.read(IOBuffer(cltxt), DataFrame, delim='|', skipto=3)
if "Limit" in names(df); rename!(df, "Limit" => "Mag"); end
if "Filt." in names(df); rename!(df, "Filt." => "Filter"); end
if "Tmid-T0" in names(df); rename!(df, "Tmid-T0" => "Time"); end
#rename!(df, "Filt." => "Filter", "Tmid-T0" => "Time")
dframe()
elseif occursin("report on behalf of the Swift/UVOT team",txt)
println(" SWIFT/UVOT report")
hb,he=findfirst(r"^Filter"im,txt)
lr,_=findnext("\n\nThe",txt,he)
cltxt=replace(txt[hb:lr], " +/- "=>s"\t", r" +(\w)"=>s"\t\1" ,r" +(>)"=>s"\t",r"\+/?- ?"=>s"\t",">"=>s"\t")
df=CSV.read(IOBuffer(cltxt), DataFrame, delim='\t')
if "Column6" in names(df); rename!(df, :Column6 => :Mag_err); end
df.Time = (df."T_start(s)" .+ df."T_stop(s)") ./2
dframe()
end # if occursin
catch e
println("error ")
#rethrow()
end # trycatch
end # for loop
println()
if !isnothing(dfg)
CSV.write("data-all.csv",dfg)
else
@info "no dfg to write"
end # !isnothing
end # function doanalysis
doanalysis()
but below code works if i provide renaming for every column.
rename!(df,["Time","Date Time","Telescope","Coord (J2000)","Filter","Exp(s)","Mag","Comment"])