I want.... to cheat...

[Maeda Toshiie]

Never thought I'd say this... but I'm playing as Takeda and pretty much own the western side of the map, Shimazu owns the eastern side and we both have massive legions guarding the borders....

Takeda died, long live the new Takeda...57 years old, 4 years later, Takeda died, long live the new Takeda...again in his late 50's, no heirs...6 years later Takeda died, long live the Ronin

Is there a cheat to produce an heir instantly ?

Short answer:

There is no cheat that can help you even if you want to use it.

Long answer:

Heirs in STW are handled differently from the later games. Each faction has a fixed set of heirs that appear at fixed times. It is always a good idea to have a heir appear in a suitable unit. Having them appear in Ashigaru units (Yari, Teppo or x-bow), No Dachi and WMs are generally a bad idea, since the Ashis are crap, ND tend to die fast while killing fast and are vulnerable to missile, and WMs are vulnerable to missile even if their melee is strong.

Generally Daimyos, unless they die on the field (not difficult to prevent) or assassination (maybe a problem if it involves Geishas but there are some measures that can be taken to help) can life to ~70. If they die of illness, reload once or twice and he should live through it, though the occurrences of these can increase. The seed for Daiymo deaths are not fixed like those for assassination attempts.