Вы можете использовать регулярные выражения для замены кода на имя:
import pandas as pd
import re
#For example use a dictionary to map codes to names
seller_dic = {102392852:'Lucas'}
for i in range(len(df['url'])):
#very careful with this, if a url doesn't have this structure it will throw
#an error, you may want to handle exceptions
code = re.search(r'seller_name=\d+&',df['url'][i]).group(0)
code = code.replace("seller_name=","")
code = code.replace("&","")
name = 'seller_name=' + seller_dic[code] + '&'
url = re.sub(r'seller_name=\d+&', name, df['url'][i])
df['url'][i] = url