While i'm having a hydrocele operation, could the surgeon just put in a penile implant?

No: Hydrocele surgery can lead to a lot of post-operative swelling which can complicate your recovery from penile implant surgery. There's also an increased risk of post-operative infection which can be devastating with an implant in place. I recommend waiting at least 6 weeks to heal from the hydrocele, then returning for the implant.

Yes: I am assuming there is a reason for your question. I would address your concern with your urologist. There are alternatives to penile implants for the treatment of erectile dysfunction.

Penile prosthesis: Inflatable penile prostheses require the placement of a pump in the scrotum. Cylinders and a reservoir are also placed. Due to the inflammation associated with hydrocele excision, your urologist may prefer not to place a prosthesis at this time although it can be done.