scale.lua

gui = {
  xlabel = { class = "label"; label = "x scale factor"; x = 0; y = 0; height = 1; width = 1;},
  ylabel = { class = "label"; label = "y scale factor"; x = 0; y = 1; height = 1; width = 1;},
  xsclf = { class = "floatedit"; name = "xsclf"; value = 1; x = 1; y = 0; height = 1; width = 1;},
  ysclf = { class = "floatedit"; name = "ysclf"; value = 1; x = 1; y = 1; height = 1; width = 1;},
}

function drawgui(sub,sel)
  local b,c = aegisub.dialog.display(gui)
  scale(sub,sel,c)
end

function scale(sub,sel,conf)
  for i,lineindex in ipairs(sel) do
    local line = sub[lineindex]
    line.text = line.text:gsub("\\fscx([%d%-%.]+)",function(a) return "\\fscx"..(tonumber(a)*conf.xsclf) end)
    line.text = line.text:gsub("\\fscy([%d%-%.]+)",function(a) return "\\fscy"..(tonumber(a)*conf.ysclf) end)
    sub[lineindex] = line
  end
end

aegisub.register_macro("Scale Lines","Scale the scales in the selected lines",drawgui)