If my previous solution does not suit you, then in order for you not to make edits to html every time, you can do it programmatically.
local browser = require("browser")
if system.getInfo("platform") == 'html5' then
print = browser.log
-------------------------------------------
-- set content width
local code = [[
let viewportMeta = document.querySelector('meta[name="viewport"]');
viewportMeta.setAttribute('content', 'width=1024');
]]
browser.JS(code)
-------------------------------------------
end