Level Description

M
You can do this in the init() of an indi, dont know if you can change it after?

if (Period()==PERIOD_H4)
{
  SetLevelValue(0, 0.00); // Same for all periods
  
  SetLevelValue(1, 2.50);
  SetLevelValue(2, -2.50);
  SetLevelValue(3, 5.00);
  SetLevelValue(4, -5.00);
  SetLevelValue(5, 10.00);
  SetLevelValue(6, -10.00);
}

if (Period()==PERIOD_D1)
{
  SetLevelValue(0, 0.00); // Same for all periods
  
  SetLevelValue(1, 10.00);
  SetLevelValue(2, -10.00);
  SetLevelValue(3, 25.00);
  SetLevelValue(4, -25.00);
  SetLevelValue(5, 50.00);
  SetLevelValue(6, -50.00);
}

Good Luck
-BB-

I take it you meant the level in subwindow for oscillator indy ranging from 0 to 100. We can put up to 32 level. Although you can just easily read the level value on the right of subwindow, I assume
you want to display it next to the Indicator Name like in some other platform... I often went to great length for convenience, here's my try... enjoy.
EDIT : A maximum of only 7 level input can be displayed. Restriction of IndicatorshortName size I suppose... but the line shows up alright.

Hello,

Have you found how to set a description for a level corresponding to indicator_levelN ? 

Use the "IndicatorSetString()" function with the "INDICATOR_LEVELTEXT"  property ID. At the first link provided, the example code is for that exact functionality, namely setting the level description.

PS! I've never used this function before, and found it by simply doing a "Search" in the MQL4 Reference documentation (hint, hint)!